* [PATCH 0/4] ex4 block bitmap prefetching @ 2020-07-17 15:53 Theodore Ts'o 2020-07-17 15:53 ` [PATCH 1/4] ext4: add prefetching for block allocation bitmaps Theodore Ts'o ` (3 more replies) 0 siblings, 4 replies; 17+ messages in thread From: Theodore Ts'o @ 2020-07-17 15:53 UTC (permalink / raw) To: Ext4 Developers List; +Cc: Alex Zhuravlev, Theodore Ts'o I've revised Alex's original block allocation prefetch changes a bit, and an option to prefetch all of the block allocation bitmaps when the file system is mounted. Please take a look... Alex Zhuravlev (2): ext4: add prefetching for block allocation bitmaps ext4: skip non-loaded groups at cr=0/1 when scanning for good groups Theodore Ts'o (2): ext4: indicate via a block bitmap read is prefetched via a tracepoint ext4: add prefetch_block_bitmaps mount options fs/ext4/balloc.c | 16 +++- fs/ext4/ext4.h | 21 +++++- fs/ext4/mballoc.c | 143 +++++++++++++++++++++++++++++++++++- fs/ext4/super.c | 51 ++++++++++--- fs/ext4/sysfs.c | 4 + include/trace/events/ext4.h | 24 +++++- 6 files changed, 236 insertions(+), 23 deletions(-) -- 2.24.1 ^ permalink raw reply [flat|nested] 17+ messages in thread
* [PATCH 1/4] ext4: add prefetching for block allocation bitmaps 2020-07-17 15:53 [PATCH 0/4] ex4 block bitmap prefetching Theodore Ts'o @ 2020-07-17 15:53 ` Theodore Ts'o 2020-07-17 21:55 ` kernel test robot 2020-07-21 7:42 ` Andreas Dilger 2020-07-17 15:53 ` [PATCH 2/4] ext4: skip non-loaded groups at cr=0/1 when scanning for good groups Theodore Ts'o ` (2 subsequent siblings) 3 siblings, 2 replies; 17+ messages in thread From: Theodore Ts'o @ 2020-07-17 15:53 UTC (permalink / raw) To: Ext4 Developers List; +Cc: Alex Zhuravlev, Andreas Dilger, Theodore Ts'o From: Alex Zhuravlev <bzzz@whamcloud.com> This should significantly improve bitmap loading, especially for flex groups as it tries to load all bitmaps within a flex.group instead of one by one synchronously. Prefetching is done in 8 * flex_bg groups, so it should be 8 read-ahead reads for a single allocating thread. At the end of allocation the thread waits for read-ahead completion and initializes buddy information so that read-aheads are not lost in case of memory pressure. At cr=0 the number of prefetching IOs is limited per allocation context to prevent a situation when mballoc loads thousands of bitmaps looking for a perfect group and ignoring groups with good chunks. Together with the patch "ext4: limit scanning of uninitialized groups" the mount time (which includes few tiny allocations) of a 1PB filesystem is reduced significantly: 0% full 50%-full unpatched patched mount time 33s 9279s 563s [ Restructured by tytso; removed the state flags in the allocation context, so it can be used to lazily prefetch the allocation bitmaps immediately after the file system is mounted. Skip prefetching block groups which are unitialized. Finally pass in the REQ_RAHEAD flag to the block layer while prefetching. ] Signed-off-by: Alex Zhuravlev <bzzz@whamcloud.com> Reviewed-by: Andreas Dilger <adilger@whamcloud.com> Signed-off-by: Theodore Ts'o <tytso@mit.edu> --- fs/ext4/balloc.c | 14 +++-- fs/ext4/ext4.h | 8 ++- fs/ext4/mballoc.c | 132 +++++++++++++++++++++++++++++++++++++++++++++- fs/ext4/sysfs.c | 4 ++ 4 files changed, 152 insertions(+), 6 deletions(-) diff --git a/fs/ext4/balloc.c b/fs/ext4/balloc.c index 1ba46d87cdf1..aaa9ec5212c8 100644 --- a/fs/ext4/balloc.c +++ b/fs/ext4/balloc.c @@ -413,7 +413,8 @@ static int ext4_validate_block_bitmap(struct super_block *sb, * Return buffer_head on success or an ERR_PTR in case of failure. */ struct buffer_head * -ext4_read_block_bitmap_nowait(struct super_block *sb, ext4_group_t block_group) +ext4_read_block_bitmap_nowait(struct super_block *sb, ext4_group_t block_group, + bool ignore_locked) { struct ext4_group_desc *desc; struct ext4_sb_info *sbi = EXT4_SB(sb); @@ -441,6 +442,12 @@ ext4_read_block_bitmap_nowait(struct super_block *sb, ext4_group_t block_group) return ERR_PTR(-ENOMEM); } + if (ignore_locked && buffer_locked(bh)) { + /* buffer under IO already, return if called for prefetching */ + put_bh(bh); + return NULL; + } + if (bitmap_uptodate(bh)) goto verify; @@ -490,7 +497,8 @@ ext4_read_block_bitmap_nowait(struct super_block *sb, ext4_group_t block_group) trace_ext4_read_block_bitmap_load(sb, block_group); bh->b_end_io = ext4_end_bitmap_read; get_bh(bh); - submit_bh(REQ_OP_READ, REQ_META | REQ_PRIO, bh); + submit_bh(REQ_OP_READ, REQ_META | REQ_PRIO | + ignore_locked ? REQ_RAHEAD : 0, bh); return bh; verify: err = ext4_validate_block_bitmap(sb, desc, block_group, bh); @@ -534,7 +542,7 @@ ext4_read_block_bitmap(struct super_block *sb, ext4_group_t block_group) struct buffer_head *bh; int err; - bh = ext4_read_block_bitmap_nowait(sb, block_group); + bh = ext4_read_block_bitmap_nowait(sb, block_group, false); if (IS_ERR(bh)) return bh; err = ext4_wait_block_bitmap(sb, block_group, bh); diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h index 42f5060f3cdf..7451662e092a 100644 --- a/fs/ext4/ext4.h +++ b/fs/ext4/ext4.h @@ -1505,6 +1505,8 @@ struct ext4_sb_info { /* where last allocation was done - for stream allocation */ unsigned long s_mb_last_group; unsigned long s_mb_last_start; + unsigned int s_mb_prefetch; + unsigned int s_mb_prefetch_limit; /* stats for buddy allocator */ atomic_t s_bal_reqs; /* number of reqs with len > 1 */ @@ -2446,7 +2448,8 @@ extern struct ext4_group_desc * ext4_get_group_desc(struct super_block * sb, extern int ext4_should_retry_alloc(struct super_block *sb, int *retries); extern struct buffer_head *ext4_read_block_bitmap_nowait(struct super_block *sb, - ext4_group_t block_group); + ext4_group_t block_group, + bool ignore_locked); extern int ext4_wait_block_bitmap(struct super_block *sb, ext4_group_t block_group, struct buffer_head *bh); @@ -3145,6 +3148,7 @@ struct ext4_group_info { (1 << EXT4_GROUP_INFO_BBITMAP_CORRUPT_BIT) #define EXT4_GROUP_INFO_IBITMAP_CORRUPT \ (1 << EXT4_GROUP_INFO_IBITMAP_CORRUPT_BIT) +#define EXT4_GROUP_INFO_BBITMAP_READ_BIT 4 #define EXT4_MB_GRP_NEED_INIT(grp) \ (test_bit(EXT4_GROUP_INFO_NEED_INIT_BIT, &((grp)->bb_state))) @@ -3159,6 +3163,8 @@ struct ext4_group_info { (set_bit(EXT4_GROUP_INFO_WAS_TRIMMED_BIT, &((grp)->bb_state))) #define EXT4_MB_GRP_CLEAR_TRIMMED(grp) \ (clear_bit(EXT4_GROUP_INFO_WAS_TRIMMED_BIT, &((grp)->bb_state))) +#define EXT4_MB_GRP_TEST_AND_SET_READ(grp) \ + (test_and_set_bit(EXT4_GROUP_INFO_BBITMAP_READ_BIT, &((grp)->bb_state))) #define EXT4_MAX_CONTENTION 8 #define EXT4_CONTENTION_THRESHOLD 2 diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c index c0a331e2feb0..8a1e6e03c088 100644 --- a/fs/ext4/mballoc.c +++ b/fs/ext4/mballoc.c @@ -922,7 +922,7 @@ static int ext4_mb_init_cache(struct page *page, char *incore, gfp_t gfp) bh[i] = NULL; continue; } - bh[i] = ext4_read_block_bitmap_nowait(sb, group); + bh[i] = ext4_read_block_bitmap_nowait(sb, group, false); if (IS_ERR(bh[i])) { err = PTR_ERR(bh[i]); bh[i] = NULL; @@ -2209,12 +2209,93 @@ static int ext4_mb_good_group_nolock(struct ext4_allocation_context *ac, return ret; } +/* + * Start prefetching @nr block bitmaps starting at @group. + * Return the next group which needs to be prefetched. + */ +static ext4_group_t +ext4_mb_prefetch(struct super_block *sb, ext4_group_t group, + unsigned int nr, int *cnt) +{ + ext4_group_t ngroups = ext4_get_groups_count(sb); + struct buffer_head *bh; + struct blk_plug plug; + + blk_start_plug(&plug); + while (nr-- > 0) { + struct ext4_group_desc *gdp = ext4_get_group_desc(sb, group, + NULL); + struct ext4_group_info *grp = ext4_get_group_info(sb, group); + + /* + * Prefetch block groups with free blocks; but don't + * bother if it is marked uninitialized on disk, since + * it won't require I/O to read. Also only try to + * prefetch once, so we avoid getblk() call, which can + * be expensive. + */ + if (!EXT4_MB_GRP_TEST_AND_SET_READ(grp) && + EXT4_MB_GRP_NEED_INIT(grp) && + ext4_free_group_clusters(sb, gdp) > 0 && + !(ext4_has_group_desc_csum(sb) && + (gdp->bg_flags & cpu_to_le16(EXT4_BG_BLOCK_UNINIT)))) { + bh = ext4_read_block_bitmap_nowait(sb, group, true); + if (bh && !IS_ERR(bh)) { + if (!buffer_uptodate(bh) && cnt) + (*cnt)++; + brelse(bh); + } + } + if (++group >= ngroups) + group = 0; + } + blk_finish_plug(&plug); + return group; +} + +/* + * Prefetching reads the block bitmap into the buffer cache; but we + * need to make sure that the buddy bitmap in the page cache has been + * initialized. Note that ext4_mb_init_group() will block if the I/O + * is not yet completed, or indeed if it was not initiated by + * ext4_mb_prefetch did not start the I/O. + * + * TODO: We should actually kick off the buddy bitmap setup in a work + * queue when the buffer I/O is completed, so that we don't block + * waiting for the block allocation bitmap read to finish when + * ext4_mb_prefetch_fini is called from ext4_mb_regular_allocator(). + */ +static void +ext4_mb_prefetch_fini(struct super_block *sb, ext4_group_t group, + unsigned int nr) +{ + while (nr-- > 0) { + struct ext4_group_desc *gdp = ext4_get_group_desc(sb, group, + NULL); + struct ext4_group_info *grp = ext4_get_group_info(sb, group); + + if (!group) + group = ext4_get_groups_count(sb); + group--; + grp = ext4_get_group_info(sb, group); + + if (EXT4_MB_GRP_NEED_INIT(grp) && + ext4_free_group_clusters(sb, gdp) > 0 && + !(ext4_has_group_desc_csum(sb) && + (gdp->bg_flags & cpu_to_le16(EXT4_BG_BLOCK_UNINIT)))) { + if (ext4_mb_init_group(sb, group, GFP_NOFS)) + break; + } + } +} + static noinline_for_stack int ext4_mb_regular_allocator(struct ext4_allocation_context *ac) { - ext4_group_t ngroups, group, i; + ext4_group_t prefetch_grp = 0, ngroups, group, i; int cr = -1; int err = 0, first_err = 0; + unsigned int nr = 0, prefetch_ios = 0; struct ext4_sb_info *sbi; struct super_block *sb; struct ext4_buddy e4b; @@ -2282,6 +2363,7 @@ ext4_mb_regular_allocator(struct ext4_allocation_context *ac) * from the goal value specified */ group = ac->ac_g_ex.fe_group; + prefetch_grp = group; for (i = 0; i < ngroups; group++, i++) { int ret = 0; @@ -2293,6 +2375,29 @@ ext4_mb_regular_allocator(struct ext4_allocation_context *ac) if (group >= ngroups) group = 0; + /* + * Batch reads of the block allocation bitmaps + * to get multiple READs in flight; limit + * prefetching at cr=0/1, otherwise mballoc can + * spend a lot of time loading imperfect groups + */ + if ((prefetch_grp == group) && + (cr > 1 || + prefetch_ios < sbi->s_mb_prefetch_limit)) { + unsigned int curr_ios = prefetch_ios; + + nr = sbi->s_mb_prefetch; + if (ext4_has_feature_flex_bg(sb)) { + nr = (group / sbi->s_mb_prefetch) * + sbi->s_mb_prefetch; + nr = nr + sbi->s_mb_prefetch - group; + } + prefetch_grp = ext4_mb_prefetch(sb, group, + nr, &prefetch_ios); + if (prefetch_ios == curr_ios) + nr = 0; + } + /* This now checks without needing the buddy page */ ret = ext4_mb_good_group_nolock(ac, group, cr); if (ret <= 0) { @@ -2367,6 +2472,10 @@ ext4_mb_regular_allocator(struct ext4_allocation_context *ac) mb_debug(sb, "Best len %d, origin len %d, ac_status %u, ac_flags 0x%x, cr %d ret %d\n", ac->ac_b_ex.fe_len, ac->ac_o_ex.fe_len, ac->ac_status, ac->ac_flags, cr, err); + + if (nr) + ext4_mb_prefetch_fini(sb, prefetch_grp, nr); + return err; } @@ -2613,6 +2722,25 @@ static int ext4_mb_init_backend(struct super_block *sb) goto err_freebuddy; } + if (ext4_has_feature_flex_bg(sb)) { + /* a single flex group is supposed to be read by a single IO */ + sbi->s_mb_prefetch = 1 << sbi->s_es->s_log_groups_per_flex; + sbi->s_mb_prefetch *= 8; /* 8 prefetch IOs in flight at most */ + } else { + sbi->s_mb_prefetch = 32; + } + if (sbi->s_mb_prefetch > ext4_get_groups_count(sb)) + sbi->s_mb_prefetch = ext4_get_groups_count(sb); + /* now many real IOs to prefetch within a single allocation at cr=0 + * given cr=0 is an CPU-related optimization we shouldn't try to + * load too many groups, at some point we should start to use what + * we've got in memory. + * with an average random access time 5ms, it'd take a second to get + * 200 groups (* N with flex_bg), so let's make this limit 4 */ + sbi->s_mb_prefetch_limit = sbi->s_mb_prefetch * 4; + if (sbi->s_mb_prefetch_limit > ext4_get_groups_count(sb)) + sbi->s_mb_prefetch_limit = ext4_get_groups_count(sb); + return 0; err_freebuddy: diff --git a/fs/ext4/sysfs.c b/fs/ext4/sysfs.c index 6c9fc9e21c13..31e0db726d21 100644 --- a/fs/ext4/sysfs.c +++ b/fs/ext4/sysfs.c @@ -240,6 +240,8 @@ EXT4_RO_ATTR_ES_STRING(last_error_func, s_last_error_func, 32); EXT4_ATTR(first_error_time, 0444, first_error_time); EXT4_ATTR(last_error_time, 0444, last_error_time); EXT4_ATTR(journal_task, 0444, journal_task); +EXT4_RW_ATTR_SBI_UI(mb_prefetch, s_mb_prefetch); +EXT4_RW_ATTR_SBI_UI(mb_prefetch_limit, s_mb_prefetch_limit); static unsigned int old_bump_val = 128; EXT4_ATTR_PTR(max_writeback_mb_bump, 0444, pointer_ui, &old_bump_val); @@ -283,6 +285,8 @@ static struct attribute *ext4_attrs[] = { #ifdef CONFIG_EXT4_DEBUG ATTR_LIST(simulate_fail), #endif + ATTR_LIST(mb_prefetch), + ATTR_LIST(mb_prefetch_limit), NULL, }; ATTRIBUTE_GROUPS(ext4); -- 2.24.1 ^ permalink raw reply related [flat|nested] 17+ messages in thread
* Re: [PATCH 1/4] ext4: add prefetching for block allocation bitmaps 2020-07-17 15:53 ` [PATCH 1/4] ext4: add prefetching for block allocation bitmaps Theodore Ts'o @ 2020-07-17 21:55 ` kernel test robot 2020-07-21 7:42 ` Andreas Dilger 1 sibling, 0 replies; 17+ messages in thread From: kernel test robot @ 2020-07-17 21:55 UTC (permalink / raw) To: Theodore Ts'o, Ext4 Developers List Cc: kbuild-all, clang-built-linux, Alex Zhuravlev, Andreas Dilger, Theodore Ts'o [-- Attachment #1: Type: text/plain, Size: 5812 bytes --] Hi Theodore, Thank you for the patch! Perhaps something to improve: [auto build test WARNING on tip/perf/core] [also build test WARNING on v5.8-rc5 next-20200717] [cannot apply to ext4/dev] [If your patch is applied to the wrong git tree, kindly drop us a note. And when submitting patch, we suggest to use '--base' as documented in https://git-scm.com/docs/git-format-patch] url: https://github.com/0day-ci/linux/commits/Theodore-Ts-o/ex4-block-bitmap-prefetching/20200718-000006 base: https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git c085fb8774671e83f6199a8e838fbc0e57094029 config: arm64-randconfig-r036-20200718 (attached as .config) compiler: clang version 12.0.0 (https://github.com/llvm/llvm-project ed6b578040a85977026c93bf4188f996148f3218) reproduce (this is a W=1 build): wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross chmod +x ~/bin/make.cross # install arm64 cross compiling tool for clang build # apt-get install binutils-aarch64-linux-gnu # save the attached .config to linux build tree COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross ARCH=arm64 If you fix the issue, kindly add following tag as appropriate Reported-by: kernel test robot <lkp@intel.com> All warnings (new ones prefixed by >>): >> fs/ext4/balloc.c:501:19: warning: operator '?:' has lower precedence than '|'; '|' will be evaluated first [-Wbitwise-conditional-parentheses] ignore_locked ? REQ_RAHEAD : 0, bh); ~~~~~~~~~~~~~ ^ fs/ext4/balloc.c:501:19: note: place parentheses around the '|' expression to silence this warning ignore_locked ? REQ_RAHEAD : 0, bh); ~~~~~~~~~~~~~ ^ fs/ext4/balloc.c:501:19: note: place parentheses around the '?:' expression to evaluate it first ignore_locked ? REQ_RAHEAD : 0, bh); ^ ( ) 1 warning generated. vim +501 fs/ext4/balloc.c 404 405 /** 406 * ext4_read_block_bitmap_nowait() 407 * @sb: super block 408 * @block_group: given block group 409 * 410 * Read the bitmap for a given block_group,and validate the 411 * bits for block/inode/inode tables are set in the bitmaps 412 * 413 * Return buffer_head on success or an ERR_PTR in case of failure. 414 */ 415 struct buffer_head * 416 ext4_read_block_bitmap_nowait(struct super_block *sb, ext4_group_t block_group, 417 bool ignore_locked) 418 { 419 struct ext4_group_desc *desc; 420 struct ext4_sb_info *sbi = EXT4_SB(sb); 421 struct buffer_head *bh; 422 ext4_fsblk_t bitmap_blk; 423 int err; 424 425 desc = ext4_get_group_desc(sb, block_group, NULL); 426 if (!desc) 427 return ERR_PTR(-EFSCORRUPTED); 428 bitmap_blk = ext4_block_bitmap(sb, desc); 429 if ((bitmap_blk <= le32_to_cpu(sbi->s_es->s_first_data_block)) || 430 (bitmap_blk >= ext4_blocks_count(sbi->s_es))) { 431 ext4_error(sb, "Invalid block bitmap block %llu in " 432 "block_group %u", bitmap_blk, block_group); 433 ext4_mark_group_bitmap_corrupted(sb, block_group, 434 EXT4_GROUP_INFO_BBITMAP_CORRUPT); 435 return ERR_PTR(-EFSCORRUPTED); 436 } 437 bh = sb_getblk(sb, bitmap_blk); 438 if (unlikely(!bh)) { 439 ext4_warning(sb, "Cannot get buffer for block bitmap - " 440 "block_group = %u, block_bitmap = %llu", 441 block_group, bitmap_blk); 442 return ERR_PTR(-ENOMEM); 443 } 444 445 if (ignore_locked && buffer_locked(bh)) { 446 /* buffer under IO already, return if called for prefetching */ 447 put_bh(bh); 448 return NULL; 449 } 450 451 if (bitmap_uptodate(bh)) 452 goto verify; 453 454 lock_buffer(bh); 455 if (bitmap_uptodate(bh)) { 456 unlock_buffer(bh); 457 goto verify; 458 } 459 ext4_lock_group(sb, block_group); 460 if (ext4_has_group_desc_csum(sb) && 461 (desc->bg_flags & cpu_to_le16(EXT4_BG_BLOCK_UNINIT))) { 462 if (block_group == 0) { 463 ext4_unlock_group(sb, block_group); 464 unlock_buffer(bh); 465 ext4_error(sb, "Block bitmap for bg 0 marked " 466 "uninitialized"); 467 err = -EFSCORRUPTED; 468 goto out; 469 } 470 err = ext4_init_block_bitmap(sb, bh, block_group, desc); 471 set_bitmap_uptodate(bh); 472 set_buffer_uptodate(bh); 473 set_buffer_verified(bh); 474 ext4_unlock_group(sb, block_group); 475 unlock_buffer(bh); 476 if (err) { 477 ext4_error(sb, "Failed to init block bitmap for group " 478 "%u: %d", block_group, err); 479 goto out; 480 } 481 goto verify; 482 } 483 ext4_unlock_group(sb, block_group); 484 if (buffer_uptodate(bh)) { 485 /* 486 * if not uninit if bh is uptodate, 487 * bitmap is also uptodate 488 */ 489 set_bitmap_uptodate(bh); 490 unlock_buffer(bh); 491 goto verify; 492 } 493 /* 494 * submit the buffer_head for reading 495 */ 496 set_buffer_new(bh); 497 trace_ext4_read_block_bitmap_load(sb, block_group); 498 bh->b_end_io = ext4_end_bitmap_read; 499 get_bh(bh); 500 submit_bh(REQ_OP_READ, REQ_META | REQ_PRIO | > 501 ignore_locked ? REQ_RAHEAD : 0, bh); 502 return bh; 503 verify: 504 err = ext4_validate_block_bitmap(sb, desc, block_group, bh); 505 if (err) 506 goto out; 507 return bh; 508 out: 509 put_bh(bh); 510 return ERR_PTR(err); 511 } 512 --- 0-DAY CI Kernel Test Service, Intel Corporation https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org [-- Attachment #2: .config.gz --] [-- Type: application/gzip, Size: 37084 bytes --] ^ permalink raw reply [flat|nested] 17+ messages in thread
* Re: [PATCH 1/4] ext4: add prefetching for block allocation bitmaps 2020-07-17 15:53 ` [PATCH 1/4] ext4: add prefetching for block allocation bitmaps Theodore Ts'o 2020-07-17 21:55 ` kernel test robot @ 2020-07-21 7:42 ` Andreas Dilger 2020-07-23 0:36 ` Shuichi Ihara 2020-07-23 15:00 ` tytso 1 sibling, 2 replies; 17+ messages in thread From: Andreas Dilger @ 2020-07-21 7:42 UTC (permalink / raw) To: Theodore Ts'o; +Cc: Ext4 Developers List, Alex Zhuravlev, Shuichi Ihara [-- Attachment #1: Type: text/plain, Size: 13656 bytes --] On Jul 17, 2020, at 9:53 AM, Theodore Ts'o <tytso@mit.edu> wrote: > > From: Alex Zhuravlev <bzzz@whamcloud.com> > > This should significantly improve bitmap loading, especially for flex > groups as it tries to load all bitmaps within a flex.group instead of > one by one synchronously. > > Prefetching is done in 8 * flex_bg groups, so it should be 8 read-ahead > reads for a single allocating thread. At the end of allocation the > thread waits for read-ahead completion and initializes buddy information > so that read-aheads are not lost in case of memory pressure. > > At cr=0 the number of prefetching IOs is limited per allocation context > to prevent a situation when mballoc loads thousands of bitmaps looking > for a perfect group and ignoring groups with good chunks. > > Together with the patch "ext4: limit scanning of uninitialized groups" > the mount time (which includes few tiny allocations) of a 1PB filesystem > is reduced significantly: > > 0% full 50%-full unpatched patched > mount time 33s 9279s 563s > > [ Restructured by tytso; removed the state flags in the allocation > context, so it can be used to lazily prefetch the allocation bitmaps > immediately after the file system is mounted. Skip prefetching > block groups which are unitialized. Finally pass in the REQ_RAHEAD > flag to the block layer while prefetching. ] > > Signed-off-by: Alex Zhuravlev <bzzz@whamcloud.com> > Reviewed-by: Andreas Dilger <adilger@whamcloud.com> I re-reviewed the patch with the changes, and it looks OK. I see that you reduced the prefetch limit from 32 to 4 group blocks, presumably to keep the latency low? It would be useful to see what impact that has on the mount time and IO performance of a large filesystem. Shuichi, do you have a properly populated large OST that you could test this? Since it is a tunable (/sys/fs/ext4/<dev>/mb_prefetch_limit), it should be possible to see the effect on allocation performance at least without recompiling the module, though this tunable only appears after mount, so you will have a chance to change it right after mount to see the effect. Given the long mount time with a bad parameter, this should not be hard to observe. Cheers, Andreas > Signed-off-by: Theodore Ts'o <tytso@mit.edu> > --- > fs/ext4/balloc.c | 14 +++-- > fs/ext4/ext4.h | 8 ++- > fs/ext4/mballoc.c | 132 +++++++++++++++++++++++++++++++++++++++++++++- > fs/ext4/sysfs.c | 4 ++ > 4 files changed, 152 insertions(+), 6 deletions(-) > > diff --git a/fs/ext4/balloc.c b/fs/ext4/balloc.c > index 1ba46d87cdf1..aaa9ec5212c8 100644 > --- a/fs/ext4/balloc.c > +++ b/fs/ext4/balloc.c > @@ -413,7 +413,8 @@ static int ext4_validate_block_bitmap(struct super_block *sb, > * Return buffer_head on success or an ERR_PTR in case of failure. > */ > struct buffer_head * > -ext4_read_block_bitmap_nowait(struct super_block *sb, ext4_group_t block_group) > +ext4_read_block_bitmap_nowait(struct super_block *sb, ext4_group_t block_group, > + bool ignore_locked) > { > struct ext4_group_desc *desc; > struct ext4_sb_info *sbi = EXT4_SB(sb); > @@ -441,6 +442,12 @@ ext4_read_block_bitmap_nowait(struct super_block *sb, ext4_group_t block_group) > return ERR_PTR(-ENOMEM); > } > > + if (ignore_locked && buffer_locked(bh)) { > + /* buffer under IO already, return if called for prefetching */ > + put_bh(bh); > + return NULL; > + } > + > if (bitmap_uptodate(bh)) > goto verify; > > @@ -490,7 +497,8 @@ ext4_read_block_bitmap_nowait(struct super_block *sb, ext4_group_t block_group) > trace_ext4_read_block_bitmap_load(sb, block_group); > bh->b_end_io = ext4_end_bitmap_read; > get_bh(bh); > - submit_bh(REQ_OP_READ, REQ_META | REQ_PRIO, bh); > + submit_bh(REQ_OP_READ, REQ_META | REQ_PRIO | > + ignore_locked ? REQ_RAHEAD : 0, bh); > return bh; > verify: > err = ext4_validate_block_bitmap(sb, desc, block_group, bh); > @@ -534,7 +542,7 @@ ext4_read_block_bitmap(struct super_block *sb, ext4_group_t block_group) > struct buffer_head *bh; > int err; > > - bh = ext4_read_block_bitmap_nowait(sb, block_group); > + bh = ext4_read_block_bitmap_nowait(sb, block_group, false); > if (IS_ERR(bh)) > return bh; > err = ext4_wait_block_bitmap(sb, block_group, bh); > diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h > index 42f5060f3cdf..7451662e092a 100644 > --- a/fs/ext4/ext4.h > +++ b/fs/ext4/ext4.h > @@ -1505,6 +1505,8 @@ struct ext4_sb_info { > /* where last allocation was done - for stream allocation */ > unsigned long s_mb_last_group; > unsigned long s_mb_last_start; > + unsigned int s_mb_prefetch; > + unsigned int s_mb_prefetch_limit; > > /* stats for buddy allocator */ > atomic_t s_bal_reqs; /* number of reqs with len > 1 */ > @@ -2446,7 +2448,8 @@ extern struct ext4_group_desc * ext4_get_group_desc(struct super_block * sb, > extern int ext4_should_retry_alloc(struct super_block *sb, int *retries); > > extern struct buffer_head *ext4_read_block_bitmap_nowait(struct super_block *sb, > - ext4_group_t block_group); > + ext4_group_t block_group, > + bool ignore_locked); > extern int ext4_wait_block_bitmap(struct super_block *sb, > ext4_group_t block_group, > struct buffer_head *bh); > @@ -3145,6 +3148,7 @@ struct ext4_group_info { > (1 << EXT4_GROUP_INFO_BBITMAP_CORRUPT_BIT) > #define EXT4_GROUP_INFO_IBITMAP_CORRUPT \ > (1 << EXT4_GROUP_INFO_IBITMAP_CORRUPT_BIT) > +#define EXT4_GROUP_INFO_BBITMAP_READ_BIT 4 > > #define EXT4_MB_GRP_NEED_INIT(grp) \ > (test_bit(EXT4_GROUP_INFO_NEED_INIT_BIT, &((grp)->bb_state))) > @@ -3159,6 +3163,8 @@ struct ext4_group_info { > (set_bit(EXT4_GROUP_INFO_WAS_TRIMMED_BIT, &((grp)->bb_state))) > #define EXT4_MB_GRP_CLEAR_TRIMMED(grp) \ > (clear_bit(EXT4_GROUP_INFO_WAS_TRIMMED_BIT, &((grp)->bb_state))) > +#define EXT4_MB_GRP_TEST_AND_SET_READ(grp) \ > + (test_and_set_bit(EXT4_GROUP_INFO_BBITMAP_READ_BIT, &((grp)->bb_state))) > > #define EXT4_MAX_CONTENTION 8 > #define EXT4_CONTENTION_THRESHOLD 2 > diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c > index c0a331e2feb0..8a1e6e03c088 100644 > --- a/fs/ext4/mballoc.c > +++ b/fs/ext4/mballoc.c > @@ -922,7 +922,7 @@ static int ext4_mb_init_cache(struct page *page, char *incore, gfp_t gfp) > bh[i] = NULL; > continue; > } > - bh[i] = ext4_read_block_bitmap_nowait(sb, group); > + bh[i] = ext4_read_block_bitmap_nowait(sb, group, false); > if (IS_ERR(bh[i])) { > err = PTR_ERR(bh[i]); > bh[i] = NULL; > @@ -2209,12 +2209,93 @@ static int ext4_mb_good_group_nolock(struct ext4_allocation_context *ac, > return ret; > } > > +/* > + * Start prefetching @nr block bitmaps starting at @group. > + * Return the next group which needs to be prefetched. > + */ > +static ext4_group_t > +ext4_mb_prefetch(struct super_block *sb, ext4_group_t group, > + unsigned int nr, int *cnt) > +{ > + ext4_group_t ngroups = ext4_get_groups_count(sb); > + struct buffer_head *bh; > + struct blk_plug plug; > + > + blk_start_plug(&plug); > + while (nr-- > 0) { > + struct ext4_group_desc *gdp = ext4_get_group_desc(sb, group, > + NULL); > + struct ext4_group_info *grp = ext4_get_group_info(sb, group); > + > + /* > + * Prefetch block groups with free blocks; but don't > + * bother if it is marked uninitialized on disk, since > + * it won't require I/O to read. Also only try to > + * prefetch once, so we avoid getblk() call, which can > + * be expensive. > + */ > + if (!EXT4_MB_GRP_TEST_AND_SET_READ(grp) && > + EXT4_MB_GRP_NEED_INIT(grp) && > + ext4_free_group_clusters(sb, gdp) > 0 && > + !(ext4_has_group_desc_csum(sb) && > + (gdp->bg_flags & cpu_to_le16(EXT4_BG_BLOCK_UNINIT)))) { > + bh = ext4_read_block_bitmap_nowait(sb, group, true); > + if (bh && !IS_ERR(bh)) { > + if (!buffer_uptodate(bh) && cnt) > + (*cnt)++; > + brelse(bh); > + } > + } > + if (++group >= ngroups) > + group = 0; > + } > + blk_finish_plug(&plug); > + return group; > +} > + > +/* > + * Prefetching reads the block bitmap into the buffer cache; but we > + * need to make sure that the buddy bitmap in the page cache has been > + * initialized. Note that ext4_mb_init_group() will block if the I/O > + * is not yet completed, or indeed if it was not initiated by > + * ext4_mb_prefetch did not start the I/O. > + * > + * TODO: We should actually kick off the buddy bitmap setup in a work > + * queue when the buffer I/O is completed, so that we don't block > + * waiting for the block allocation bitmap read to finish when > + * ext4_mb_prefetch_fini is called from ext4_mb_regular_allocator(). > + */ > +static void > +ext4_mb_prefetch_fini(struct super_block *sb, ext4_group_t group, > + unsigned int nr) > +{ > + while (nr-- > 0) { > + struct ext4_group_desc *gdp = ext4_get_group_desc(sb, group, > + NULL); > + struct ext4_group_info *grp = ext4_get_group_info(sb, group); > + > + if (!group) > + group = ext4_get_groups_count(sb); > + group--; > + grp = ext4_get_group_info(sb, group); > + > + if (EXT4_MB_GRP_NEED_INIT(grp) && > + ext4_free_group_clusters(sb, gdp) > 0 && > + !(ext4_has_group_desc_csum(sb) && > + (gdp->bg_flags & cpu_to_le16(EXT4_BG_BLOCK_UNINIT)))) { > + if (ext4_mb_init_group(sb, group, GFP_NOFS)) > + break; > + } > + } > +} > + > static noinline_for_stack int > ext4_mb_regular_allocator(struct ext4_allocation_context *ac) > { > - ext4_group_t ngroups, group, i; > + ext4_group_t prefetch_grp = 0, ngroups, group, i; > int cr = -1; > int err = 0, first_err = 0; > + unsigned int nr = 0, prefetch_ios = 0; > struct ext4_sb_info *sbi; > struct super_block *sb; > struct ext4_buddy e4b; > @@ -2282,6 +2363,7 @@ ext4_mb_regular_allocator(struct ext4_allocation_context *ac) > * from the goal value specified > */ > group = ac->ac_g_ex.fe_group; > + prefetch_grp = group; > > for (i = 0; i < ngroups; group++, i++) { > int ret = 0; > @@ -2293,6 +2375,29 @@ ext4_mb_regular_allocator(struct ext4_allocation_context *ac) > if (group >= ngroups) > group = 0; > > + /* > + * Batch reads of the block allocation bitmaps > + * to get multiple READs in flight; limit > + * prefetching at cr=0/1, otherwise mballoc can > + * spend a lot of time loading imperfect groups > + */ > + if ((prefetch_grp == group) && > + (cr > 1 || > + prefetch_ios < sbi->s_mb_prefetch_limit)) { > + unsigned int curr_ios = prefetch_ios; > + > + nr = sbi->s_mb_prefetch; > + if (ext4_has_feature_flex_bg(sb)) { > + nr = (group / sbi->s_mb_prefetch) * > + sbi->s_mb_prefetch; > + nr = nr + sbi->s_mb_prefetch - group; > + } > + prefetch_grp = ext4_mb_prefetch(sb, group, > + nr, &prefetch_ios); > + if (prefetch_ios == curr_ios) > + nr = 0; > + } > + > /* This now checks without needing the buddy page */ > ret = ext4_mb_good_group_nolock(ac, group, cr); > if (ret <= 0) { > @@ -2367,6 +2472,10 @@ ext4_mb_regular_allocator(struct ext4_allocation_context *ac) > mb_debug(sb, "Best len %d, origin len %d, ac_status %u, ac_flags 0x%x, cr %d ret %d\n", > ac->ac_b_ex.fe_len, ac->ac_o_ex.fe_len, ac->ac_status, > ac->ac_flags, cr, err); > + > + if (nr) > + ext4_mb_prefetch_fini(sb, prefetch_grp, nr); > + > return err; > } > > @@ -2613,6 +2722,25 @@ static int ext4_mb_init_backend(struct super_block *sb) > goto err_freebuddy; > } > > + if (ext4_has_feature_flex_bg(sb)) { > + /* a single flex group is supposed to be read by a single IO */ > + sbi->s_mb_prefetch = 1 << sbi->s_es->s_log_groups_per_flex; > + sbi->s_mb_prefetch *= 8; /* 8 prefetch IOs in flight at most */ > + } else { > + sbi->s_mb_prefetch = 32; > + } > + if (sbi->s_mb_prefetch > ext4_get_groups_count(sb)) > + sbi->s_mb_prefetch = ext4_get_groups_count(sb); > + /* now many real IOs to prefetch within a single allocation at cr=0 > + * given cr=0 is an CPU-related optimization we shouldn't try to > + * load too many groups, at some point we should start to use what > + * we've got in memory. > + * with an average random access time 5ms, it'd take a second to get > + * 200 groups (* N with flex_bg), so let's make this limit 4 */ > + sbi->s_mb_prefetch_limit = sbi->s_mb_prefetch * 4; > + if (sbi->s_mb_prefetch_limit > ext4_get_groups_count(sb)) > + sbi->s_mb_prefetch_limit = ext4_get_groups_count(sb); > + > return 0; > > err_freebuddy: > diff --git a/fs/ext4/sysfs.c b/fs/ext4/sysfs.c > index 6c9fc9e21c13..31e0db726d21 100644 > --- a/fs/ext4/sysfs.c > +++ b/fs/ext4/sysfs.c > @@ -240,6 +240,8 @@ EXT4_RO_ATTR_ES_STRING(last_error_func, s_last_error_func, 32); > EXT4_ATTR(first_error_time, 0444, first_error_time); > EXT4_ATTR(last_error_time, 0444, last_error_time); > EXT4_ATTR(journal_task, 0444, journal_task); > +EXT4_RW_ATTR_SBI_UI(mb_prefetch, s_mb_prefetch); > +EXT4_RW_ATTR_SBI_UI(mb_prefetch_limit, s_mb_prefetch_limit); > > static unsigned int old_bump_val = 128; > EXT4_ATTR_PTR(max_writeback_mb_bump, 0444, pointer_ui, &old_bump_val); > @@ -283,6 +285,8 @@ static struct attribute *ext4_attrs[] = { > #ifdef CONFIG_EXT4_DEBUG > ATTR_LIST(simulate_fail), > #endif > + ATTR_LIST(mb_prefetch), > + ATTR_LIST(mb_prefetch_limit), > NULL, > }; > ATTRIBUTE_GROUPS(ext4); > -- > 2.24.1 > Cheers, Andreas [-- Attachment #2: Message signed with OpenPGP --] [-- Type: application/pgp-signature, Size: 873 bytes --] ^ permalink raw reply [flat|nested] 17+ messages in thread
* Re: [PATCH 1/4] ext4: add prefetching for block allocation bitmaps 2020-07-21 7:42 ` Andreas Dilger @ 2020-07-23 0:36 ` Shuichi Ihara 2020-07-23 15:00 ` tytso 1 sibling, 0 replies; 17+ messages in thread From: Shuichi Ihara @ 2020-07-23 0:36 UTC (permalink / raw) To: Andreas Dilger; +Cc: Theodore Ts'o, Ext4 Developers List, Alex Zhuravlev Hi Andreas, > Shuichi, do you have a properly populated large OST that you could test > this? Since it is a tunable (/sys/fs/ext4/<dev>/mb_prefetch_limit), it > should be possible to see the effect on allocation performance at least > without recompiling the module, though this tunable only appears after > mount, so you will have a chance to change it right after mount to see > the effect. Given the long mount time with a bad parameter, this should > not be hard to observe. Sure, I will test this on large OST and check if there are any good/bad performance impacts with it. Thanks Ihara > On Jul 21, 2020, at 16:42, Andreas Dilger <adilger@dilger.ca> wrote: > > On Jul 17, 2020, at 9:53 AM, Theodore Ts'o <tytso@mit.edu> wrote: >> >> From: Alex Zhuravlev <bzzz@whamcloud.com> >> >> This should significantly improve bitmap loading, especially for flex >> groups as it tries to load all bitmaps within a flex.group instead of >> one by one synchronously. >> >> Prefetching is done in 8 * flex_bg groups, so it should be 8 read-ahead >> reads for a single allocating thread. At the end of allocation the >> thread waits for read-ahead completion and initializes buddy information >> so that read-aheads are not lost in case of memory pressure. >> >> At cr=0 the number of prefetching IOs is limited per allocation context >> to prevent a situation when mballoc loads thousands of bitmaps looking >> for a perfect group and ignoring groups with good chunks. >> >> Together with the patch "ext4: limit scanning of uninitialized groups" >> the mount time (which includes few tiny allocations) of a 1PB filesystem >> is reduced significantly: >> >> 0% full 50%-full unpatched patched >> mount time 33s 9279s 563s >> >> [ Restructured by tytso; removed the state flags in the allocation >> context, so it can be used to lazily prefetch the allocation bitmaps >> immediately after the file system is mounted. Skip prefetching >> block groups which are unitialized. Finally pass in the REQ_RAHEAD >> flag to the block layer while prefetching. ] >> >> Signed-off-by: Alex Zhuravlev <bzzz@whamcloud.com> >> Reviewed-by: Andreas Dilger <adilger@whamcloud.com> > > I re-reviewed the patch with the changes, and it looks OK. I see that > you reduced the prefetch limit from 32 to 4 group blocks, presumably to > keep the latency low? It would be useful to see what impact that has > on the mount time and IO performance of a large filesystem. > > Shuichi, do you have a properly populated large OST that you could test > this? Since it is a tunable (/sys/fs/ext4/<dev>/mb_prefetch_limit), it > should be possible to see the effect on allocation performance at least > without recompiling the module, though this tunable only appears after > mount, so you will have a chance to change it right after mount to see > the effect. Given the long mount time with a bad parameter, this should > not be hard to observe. > > Cheers, Andreas > >> Signed-off-by: Theodore Ts'o <tytso@mit.edu> >> --- >> fs/ext4/balloc.c | 14 +++-- >> fs/ext4/ext4.h | 8 ++- >> fs/ext4/mballoc.c | 132 +++++++++++++++++++++++++++++++++++++++++++++- >> fs/ext4/sysfs.c | 4 ++ >> 4 files changed, 152 insertions(+), 6 deletions(-) >> >> diff --git a/fs/ext4/balloc.c b/fs/ext4/balloc.c >> index 1ba46d87cdf1..aaa9ec5212c8 100644 >> --- a/fs/ext4/balloc.c >> +++ b/fs/ext4/balloc.c >> @@ -413,7 +413,8 @@ static int ext4_validate_block_bitmap(struct super_block *sb, >> * Return buffer_head on success or an ERR_PTR in case of failure. >> */ >> struct buffer_head * >> -ext4_read_block_bitmap_nowait(struct super_block *sb, ext4_group_t block_group) >> +ext4_read_block_bitmap_nowait(struct super_block *sb, ext4_group_t block_group, >> + bool ignore_locked) >> { >> struct ext4_group_desc *desc; >> struct ext4_sb_info *sbi = EXT4_SB(sb); >> @@ -441,6 +442,12 @@ ext4_read_block_bitmap_nowait(struct super_block *sb, ext4_group_t block_group) >> return ERR_PTR(-ENOMEM); >> } >> >> + if (ignore_locked && buffer_locked(bh)) { >> + /* buffer under IO already, return if called for prefetching */ >> + put_bh(bh); >> + return NULL; >> + } >> + >> if (bitmap_uptodate(bh)) >> goto verify; >> >> @@ -490,7 +497,8 @@ ext4_read_block_bitmap_nowait(struct super_block *sb, ext4_group_t block_group) >> trace_ext4_read_block_bitmap_load(sb, block_group); >> bh->b_end_io = ext4_end_bitmap_read; >> get_bh(bh); >> - submit_bh(REQ_OP_READ, REQ_META | REQ_PRIO, bh); >> + submit_bh(REQ_OP_READ, REQ_META | REQ_PRIO | >> + ignore_locked ? REQ_RAHEAD : 0, bh); >> return bh; >> verify: >> err = ext4_validate_block_bitmap(sb, desc, block_group, bh); >> @@ -534,7 +542,7 @@ ext4_read_block_bitmap(struct super_block *sb, ext4_group_t block_group) >> struct buffer_head *bh; >> int err; >> >> - bh = ext4_read_block_bitmap_nowait(sb, block_group); >> + bh = ext4_read_block_bitmap_nowait(sb, block_group, false); >> if (IS_ERR(bh)) >> return bh; >> err = ext4_wait_block_bitmap(sb, block_group, bh); >> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h >> index 42f5060f3cdf..7451662e092a 100644 >> --- a/fs/ext4/ext4.h >> +++ b/fs/ext4/ext4.h >> @@ -1505,6 +1505,8 @@ struct ext4_sb_info { >> /* where last allocation was done - for stream allocation */ >> unsigned long s_mb_last_group; >> unsigned long s_mb_last_start; >> + unsigned int s_mb_prefetch; >> + unsigned int s_mb_prefetch_limit; >> >> /* stats for buddy allocator */ >> atomic_t s_bal_reqs; /* number of reqs with len > 1 */ >> @@ -2446,7 +2448,8 @@ extern struct ext4_group_desc * ext4_get_group_desc(struct super_block * sb, >> extern int ext4_should_retry_alloc(struct super_block *sb, int *retries); >> >> extern struct buffer_head *ext4_read_block_bitmap_nowait(struct super_block *sb, >> - ext4_group_t block_group); >> + ext4_group_t block_group, >> + bool ignore_locked); >> extern int ext4_wait_block_bitmap(struct super_block *sb, >> ext4_group_t block_group, >> struct buffer_head *bh); >> @@ -3145,6 +3148,7 @@ struct ext4_group_info { >> (1 << EXT4_GROUP_INFO_BBITMAP_CORRUPT_BIT) >> #define EXT4_GROUP_INFO_IBITMAP_CORRUPT \ >> (1 << EXT4_GROUP_INFO_IBITMAP_CORRUPT_BIT) >> +#define EXT4_GROUP_INFO_BBITMAP_READ_BIT 4 >> >> #define EXT4_MB_GRP_NEED_INIT(grp) \ >> (test_bit(EXT4_GROUP_INFO_NEED_INIT_BIT, &((grp)->bb_state))) >> @@ -3159,6 +3163,8 @@ struct ext4_group_info { >> (set_bit(EXT4_GROUP_INFO_WAS_TRIMMED_BIT, &((grp)->bb_state))) >> #define EXT4_MB_GRP_CLEAR_TRIMMED(grp) \ >> (clear_bit(EXT4_GROUP_INFO_WAS_TRIMMED_BIT, &((grp)->bb_state))) >> +#define EXT4_MB_GRP_TEST_AND_SET_READ(grp) \ >> + (test_and_set_bit(EXT4_GROUP_INFO_BBITMAP_READ_BIT, &((grp)->bb_state))) >> >> #define EXT4_MAX_CONTENTION 8 >> #define EXT4_CONTENTION_THRESHOLD 2 >> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c >> index c0a331e2feb0..8a1e6e03c088 100644 >> --- a/fs/ext4/mballoc.c >> +++ b/fs/ext4/mballoc.c >> @@ -922,7 +922,7 @@ static int ext4_mb_init_cache(struct page *page, char *incore, gfp_t gfp) >> bh[i] = NULL; >> continue; >> } >> - bh[i] = ext4_read_block_bitmap_nowait(sb, group); >> + bh[i] = ext4_read_block_bitmap_nowait(sb, group, false); >> if (IS_ERR(bh[i])) { >> err = PTR_ERR(bh[i]); >> bh[i] = NULL; >> @@ -2209,12 +2209,93 @@ static int ext4_mb_good_group_nolock(struct ext4_allocation_context *ac, >> return ret; >> } >> >> +/* >> + * Start prefetching @nr block bitmaps starting at @group. >> + * Return the next group which needs to be prefetched. >> + */ >> +static ext4_group_t >> +ext4_mb_prefetch(struct super_block *sb, ext4_group_t group, >> + unsigned int nr, int *cnt) >> +{ >> + ext4_group_t ngroups = ext4_get_groups_count(sb); >> + struct buffer_head *bh; >> + struct blk_plug plug; >> + >> + blk_start_plug(&plug); >> + while (nr-- > 0) { >> + struct ext4_group_desc *gdp = ext4_get_group_desc(sb, group, >> + NULL); >> + struct ext4_group_info *grp = ext4_get_group_info(sb, group); >> + >> + /* >> + * Prefetch block groups with free blocks; but don't >> + * bother if it is marked uninitialized on disk, since >> + * it won't require I/O to read. Also only try to >> + * prefetch once, so we avoid getblk() call, which can >> + * be expensive. >> + */ >> + if (!EXT4_MB_GRP_TEST_AND_SET_READ(grp) && >> + EXT4_MB_GRP_NEED_INIT(grp) && >> + ext4_free_group_clusters(sb, gdp) > 0 && >> + !(ext4_has_group_desc_csum(sb) && >> + (gdp->bg_flags & cpu_to_le16(EXT4_BG_BLOCK_UNINIT)))) { >> + bh = ext4_read_block_bitmap_nowait(sb, group, true); >> + if (bh && !IS_ERR(bh)) { >> + if (!buffer_uptodate(bh) && cnt) >> + (*cnt)++; >> + brelse(bh); >> + } >> + } >> + if (++group >= ngroups) >> + group = 0; >> + } >> + blk_finish_plug(&plug); >> + return group; >> +} >> + >> +/* >> + * Prefetching reads the block bitmap into the buffer cache; but we >> + * need to make sure that the buddy bitmap in the page cache has been >> + * initialized. Note that ext4_mb_init_group() will block if the I/O >> + * is not yet completed, or indeed if it was not initiated by >> + * ext4_mb_prefetch did not start the I/O. >> + * >> + * TODO: We should actually kick off the buddy bitmap setup in a work >> + * queue when the buffer I/O is completed, so that we don't block >> + * waiting for the block allocation bitmap read to finish when >> + * ext4_mb_prefetch_fini is called from ext4_mb_regular_allocator(). >> + */ >> +static void >> +ext4_mb_prefetch_fini(struct super_block *sb, ext4_group_t group, >> + unsigned int nr) >> +{ >> + while (nr-- > 0) { >> + struct ext4_group_desc *gdp = ext4_get_group_desc(sb, group, >> + NULL); >> + struct ext4_group_info *grp = ext4_get_group_info(sb, group); >> + >> + if (!group) >> + group = ext4_get_groups_count(sb); >> + group--; >> + grp = ext4_get_group_info(sb, group); >> + >> + if (EXT4_MB_GRP_NEED_INIT(grp) && >> + ext4_free_group_clusters(sb, gdp) > 0 && >> + !(ext4_has_group_desc_csum(sb) && >> + (gdp->bg_flags & cpu_to_le16(EXT4_BG_BLOCK_UNINIT)))) { >> + if (ext4_mb_init_group(sb, group, GFP_NOFS)) >> + break; >> + } >> + } >> +} >> + >> static noinline_for_stack int >> ext4_mb_regular_allocator(struct ext4_allocation_context *ac) >> { >> - ext4_group_t ngroups, group, i; >> + ext4_group_t prefetch_grp = 0, ngroups, group, i; >> int cr = -1; >> int err = 0, first_err = 0; >> + unsigned int nr = 0, prefetch_ios = 0; >> struct ext4_sb_info *sbi; >> struct super_block *sb; >> struct ext4_buddy e4b; >> @@ -2282,6 +2363,7 @@ ext4_mb_regular_allocator(struct ext4_allocation_context *ac) >> * from the goal value specified >> */ >> group = ac->ac_g_ex.fe_group; >> + prefetch_grp = group; >> >> for (i = 0; i < ngroups; group++, i++) { >> int ret = 0; >> @@ -2293,6 +2375,29 @@ ext4_mb_regular_allocator(struct ext4_allocation_context *ac) >> if (group >= ngroups) >> group = 0; >> >> + /* >> + * Batch reads of the block allocation bitmaps >> + * to get multiple READs in flight; limit >> + * prefetching at cr=0/1, otherwise mballoc can >> + * spend a lot of time loading imperfect groups >> + */ >> + if ((prefetch_grp == group) && >> + (cr > 1 || >> + prefetch_ios < sbi->s_mb_prefetch_limit)) { >> + unsigned int curr_ios = prefetch_ios; >> + >> + nr = sbi->s_mb_prefetch; >> + if (ext4_has_feature_flex_bg(sb)) { >> + nr = (group / sbi->s_mb_prefetch) * >> + sbi->s_mb_prefetch; >> + nr = nr + sbi->s_mb_prefetch - group; >> + } >> + prefetch_grp = ext4_mb_prefetch(sb, group, >> + nr, &prefetch_ios); >> + if (prefetch_ios == curr_ios) >> + nr = 0; >> + } >> + >> /* This now checks without needing the buddy page */ >> ret = ext4_mb_good_group_nolock(ac, group, cr); >> if (ret <= 0) { >> @@ -2367,6 +2472,10 @@ ext4_mb_regular_allocator(struct ext4_allocation_context *ac) >> mb_debug(sb, "Best len %d, origin len %d, ac_status %u, ac_flags 0x%x, cr %d ret %d\n", >> ac->ac_b_ex.fe_len, ac->ac_o_ex.fe_len, ac->ac_status, >> ac->ac_flags, cr, err); >> + >> + if (nr) >> + ext4_mb_prefetch_fini(sb, prefetch_grp, nr); >> + >> return err; >> } >> >> @@ -2613,6 +2722,25 @@ static int ext4_mb_init_backend(struct super_block *sb) >> goto err_freebuddy; >> } >> >> + if (ext4_has_feature_flex_bg(sb)) { >> + /* a single flex group is supposed to be read by a single IO */ >> + sbi->s_mb_prefetch = 1 << sbi->s_es->s_log_groups_per_flex; >> + sbi->s_mb_prefetch *= 8; /* 8 prefetch IOs in flight at most */ >> + } else { >> + sbi->s_mb_prefetch = 32; >> + } >> + if (sbi->s_mb_prefetch > ext4_get_groups_count(sb)) >> + sbi->s_mb_prefetch = ext4_get_groups_count(sb); >> + /* now many real IOs to prefetch within a single allocation at cr=0 >> + * given cr=0 is an CPU-related optimization we shouldn't try to >> + * load too many groups, at some point we should start to use what >> + * we've got in memory. >> + * with an average random access time 5ms, it'd take a second to get >> + * 200 groups (* N with flex_bg), so let's make this limit 4 */ >> + sbi->s_mb_prefetch_limit = sbi->s_mb_prefetch * 4; >> + if (sbi->s_mb_prefetch_limit > ext4_get_groups_count(sb)) >> + sbi->s_mb_prefetch_limit = ext4_get_groups_count(sb); >> + >> return 0; >> >> err_freebuddy: >> diff --git a/fs/ext4/sysfs.c b/fs/ext4/sysfs.c >> index 6c9fc9e21c13..31e0db726d21 100644 >> --- a/fs/ext4/sysfs.c >> +++ b/fs/ext4/sysfs.c >> @@ -240,6 +240,8 @@ EXT4_RO_ATTR_ES_STRING(last_error_func, s_last_error_func, 32); >> EXT4_ATTR(first_error_time, 0444, first_error_time); >> EXT4_ATTR(last_error_time, 0444, last_error_time); >> EXT4_ATTR(journal_task, 0444, journal_task); >> +EXT4_RW_ATTR_SBI_UI(mb_prefetch, s_mb_prefetch); >> +EXT4_RW_ATTR_SBI_UI(mb_prefetch_limit, s_mb_prefetch_limit); >> >> static unsigned int old_bump_val = 128; >> EXT4_ATTR_PTR(max_writeback_mb_bump, 0444, pointer_ui, &old_bump_val); >> @@ -283,6 +285,8 @@ static struct attribute *ext4_attrs[] = { >> #ifdef CONFIG_EXT4_DEBUG >> ATTR_LIST(simulate_fail), >> #endif >> + ATTR_LIST(mb_prefetch), >> + ATTR_LIST(mb_prefetch_limit), >> NULL, >> }; >> ATTRIBUTE_GROUPS(ext4); >> -- >> 2.24.1 >> > > > Cheers, Andreas > > > > > ^ permalink raw reply [flat|nested] 17+ messages in thread
* Re: [PATCH 1/4] ext4: add prefetching for block allocation bitmaps 2020-07-21 7:42 ` Andreas Dilger 2020-07-23 0:36 ` Shuichi Ihara @ 2020-07-23 15:00 ` tytso 1 sibling, 0 replies; 17+ messages in thread From: tytso @ 2020-07-23 15:00 UTC (permalink / raw) To: Andreas Dilger; +Cc: Ext4 Developers List, Alex Zhuravlev, Shuichi Ihara On Tue, Jul 21, 2020 at 01:42:54AM -0600, Andreas Dilger wrote: > > I re-reviewed the patch with the changes, and it looks OK. I see that > you reduced the prefetch limit from 32 to 4 group blocks, presumably to > keep the latency low? It would be useful to see what impact that has > on the mount time and IO performance of a large filesystem. No, I didn't change it. As before, it's 4 times the size of the flex_bg size (assuming the file system has flex bg's enabled); otherwise it's 128 (4 times 32). I'm actually worried that this is too aggressive on storage devies where LBA's which are adjacent to each other aren't necessarily adjacent to each other on the physical storage device. For example, on dm-thin, some qemu-img formats, and potentially some cloud virtual block devices.... Unfortunately, there isn't a good way to query a block device to determine whether adjacent LBA's are really adjacent in the real world. - Ted ^ permalink raw reply [flat|nested] 17+ messages in thread
* [PATCH 2/4] ext4: skip non-loaded groups at cr=0/1 when scanning for good groups 2020-07-17 15:53 [PATCH 0/4] ex4 block bitmap prefetching Theodore Ts'o 2020-07-17 15:53 ` [PATCH 1/4] ext4: add prefetching for block allocation bitmaps Theodore Ts'o @ 2020-07-17 15:53 ` Theodore Ts'o 2020-07-21 7:48 ` Andreas Dilger 2020-07-24 11:27 ` Благодаренко Артём 2020-07-17 15:53 ` [PATCH 3/4] ext4: indicate via a block bitmap read is prefetched via a tracepoint Theodore Ts'o 2020-07-17 15:53 ` [PATCH 4/4] ext4: add prefetch_block_bitmaps mount options Theodore Ts'o 3 siblings, 2 replies; 17+ messages in thread From: Theodore Ts'o @ 2020-07-17 15:53 UTC (permalink / raw) To: Ext4 Developers List; +Cc: Alex Zhuravlev, Alex Zhuravlev, Andreas Dilger From: Alex Zhuravlev <azhuravlev@whamcloud.com> cr=0 is supposed to be an optimization to save CPU cycles, but if buddy data (in memory) is not initialized then all this makes no sense as we have to do sync IO taking a lot of cycles. also, at cr=0 mballoc doesn't store any avaibale chunk. cr=1 also skips groups using heuristic based on avg. fragment size. it's more useful to skip such groups and switch to cr=2 where groups will be scanned for available chunks. using sparse image and dm-slow virtual device of 120TB was simulated. then the image was formatted and filled using debugfs to mark ~85% of available space as busy. mount process w/o the patch couldn't complete in half an hour (according to vmstat it would take ~10-11 hours). With the patch applied mount took ~20 seconds. Lustre-bug-id: https://jira.whamcloud.com/browse/LU-12988 Signed-off-by: Alex Zhuravlev <bzzz@whamcloud.com> Reviewed-by: Andreas Dilger <adilger@whamcloud.com> --- fs/ext4/mballoc.c | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-) diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c index 8a1e6e03c088..172994349bf6 100644 --- a/fs/ext4/mballoc.c +++ b/fs/ext4/mballoc.c @@ -2195,7 +2195,18 @@ static int ext4_mb_good_group_nolock(struct ext4_allocation_context *ac, /* We only do this if the grp has never been initialized */ if (unlikely(EXT4_MB_GRP_NEED_INIT(grp))) { - ret = ext4_mb_init_group(ac->ac_sb, group, GFP_NOFS); + struct ext4_group_desc *gdp = ext4_get_group_desc(sb, group, + NULL); + int ret; + + /* cr=0/1 is a very optimistic search to find large + * good chunks almost for free. if buddy data is + * not ready, then this optimization makes no sense */ + if (cr < 2 && + !(ext4_has_group_desc_csum(sb) && + (gdp->bg_flags & cpu_to_le16(EXT4_BG_BLOCK_UNINIT)))) + return 0; + ret = ext4_mb_init_group(sb, group, GFP_NOFS); if (ret) return ret; } -- 2.24.1 ^ permalink raw reply related [flat|nested] 17+ messages in thread
* Re: [PATCH 2/4] ext4: skip non-loaded groups at cr=0/1 when scanning for good groups 2020-07-17 15:53 ` [PATCH 2/4] ext4: skip non-loaded groups at cr=0/1 when scanning for good groups Theodore Ts'o @ 2020-07-21 7:48 ` Andreas Dilger 2020-07-24 11:27 ` Благодаренко Артём 1 sibling, 0 replies; 17+ messages in thread From: Andreas Dilger @ 2020-07-21 7:48 UTC (permalink / raw) To: Theodore Ts'o; +Cc: Ext4 Developers List, Alex Zhuravlev [-- Attachment #1: Type: text/plain, Size: 2515 bytes --] > On Jul 17, 2020, at 9:53 AM, Theodore Ts'o <tytso@mit.edu> wrote: > > From: Alex Zhuravlev <azhuravlev@whamcloud.com> > > cr=0 is supposed to be an optimization to save CPU cycles, but if > buddy data (in memory) is not initialized then all this makes no sense > as we have to do sync IO taking a lot of cycles. also, at cr=0 > mballoc doesn't store any avaibale chunk. cr=1 also skips groups using (typo) "available", but "doesn't store any available chunk" is still a bit confusing. Maybe "doesn't *choose* any available chunk"? > heuristic based on avg. fragment size. it's more useful to skip such > groups and switch to cr=2 where groups will be scanned for available > chunks. > > using sparse image and dm-slow virtual device of 120TB was > simulated. then the image was formatted and filled using debugfs to > mark ~85% of available space as busy. mount process w/o the patch > couldn't complete in half an hour (according to vmstat it would take > ~10-11 hours). With the patch applied mount took ~20 seconds. > > Lustre-bug-id: https://jira.whamcloud.com/browse/LU-12988 > Signed-off-by: Alex Zhuravlev <bzzz@whamcloud.com> > Reviewed-by: Andreas Dilger <adilger@whamcloud.com> Purely cosmetic fix below, but still fine otherwise. > --- > fs/ext4/mballoc.c | 13 ++++++++++++- > 1 file changed, 12 insertions(+), 1 deletion(-) > > diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c > index 8a1e6e03c088..172994349bf6 100644 > --- a/fs/ext4/mballoc.c > +++ b/fs/ext4/mballoc.c > @@ -2195,7 +2195,18 @@ static int ext4_mb_good_group_nolock(struct ext4_allocation_context *ac, > > /* We only do this if the grp has never been initialized */ > if (unlikely(EXT4_MB_GRP_NEED_INIT(grp))) { > - ret = ext4_mb_init_group(ac->ac_sb, group, GFP_NOFS); > + struct ext4_group_desc *gdp = ext4_get_group_desc(sb, group, > + NULL); > + int ret; (style) this might be nicer to read like: struct ext4_group_desc *gdp = ext4_get_group_desc(sb, group, NULL); int ret; > + /* cr=0/1 is a very optimistic search to find large > + * good chunks almost for free. if buddy data is > + * not ready, then this optimization makes no sense */ > + if (cr < 2 && > + !(ext4_has_group_desc_csum(sb) && > + (gdp->bg_flags & cpu_to_le16(EXT4_BG_BLOCK_UNINIT)))) > + return 0; > + ret = ext4_mb_init_group(sb, group, GFP_NOFS); > if (ret) > return ret; > } > -- > 2.24.1 > Cheers, Andreas [-- Attachment #2: Message signed with OpenPGP --] [-- Type: application/pgp-signature, Size: 873 bytes --] ^ permalink raw reply [flat|nested] 17+ messages in thread
* Re: [PATCH 2/4] ext4: skip non-loaded groups at cr=0/1 when scanning for good groups 2020-07-17 15:53 ` [PATCH 2/4] ext4: skip non-loaded groups at cr=0/1 when scanning for good groups Theodore Ts'o 2020-07-21 7:48 ` Andreas Dilger @ 2020-07-24 11:27 ` Благодаренко Артём 1 sibling, 0 replies; 17+ messages in thread From: Благодаренко Артём @ 2020-07-24 11:27 UTC (permalink / raw) To: Theodore Ts'o Cc: Ext4 Developers List, Alex Zhuravlev, Alex Zhuravlev, Andreas Dilger Looks good. Reviewed-by: Artem Blagodarenko <artem.blagodarenko@gmail.com> > On 17 Jul 2020, at 18:53, Theodore Ts'o <tytso@mit.edu> wrote: > > From: Alex Zhuravlev <azhuravlev@whamcloud.com> > > cr=0 is supposed to be an optimization to save CPU cycles, but if > buddy data (in memory) is not initialized then all this makes no sense > as we have to do sync IO taking a lot of cycles. also, at cr=0 > mballoc doesn't store any avaibale chunk. cr=1 also skips groups using > heuristic based on avg. fragment size. it's more useful to skip such > groups and switch to cr=2 where groups will be scanned for available > chunks. > > using sparse image and dm-slow virtual device of 120TB was > simulated. then the image was formatted and filled using debugfs to > mark ~85% of available space as busy. mount process w/o the patch > couldn't complete in half an hour (according to vmstat it would take > ~10-11 hours). With the patch applied mount took ~20 seconds. > > Lustre-bug-id: https://jira.whamcloud.com/browse/LU-12988 > Signed-off-by: Alex Zhuravlev <bzzz@whamcloud.com> > Reviewed-by: Andreas Dilger <adilger@whamcloud.com> > --- > fs/ext4/mballoc.c | 13 ++++++++++++- > 1 file changed, 12 insertions(+), 1 deletion(-) > > diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c > index 8a1e6e03c088..172994349bf6 100644 > --- a/fs/ext4/mballoc.c > +++ b/fs/ext4/mballoc.c > @@ -2195,7 +2195,18 @@ static int ext4_mb_good_group_nolock(struct ext4_allocation_context *ac, > > /* We only do this if the grp has never been initialized */ > if (unlikely(EXT4_MB_GRP_NEED_INIT(grp))) { > - ret = ext4_mb_init_group(ac->ac_sb, group, GFP_NOFS); > + struct ext4_group_desc *gdp = ext4_get_group_desc(sb, group, > + NULL); > + int ret; > + > + /* cr=0/1 is a very optimistic search to find large > + * good chunks almost for free. if buddy data is > + * not ready, then this optimization makes no sense */ > + if (cr < 2 && > + !(ext4_has_group_desc_csum(sb) && > + (gdp->bg_flags & cpu_to_le16(EXT4_BG_BLOCK_UNINIT)))) > + return 0; > + ret = ext4_mb_init_group(sb, group, GFP_NOFS); > if (ret) > return ret; > } > -- > 2.24.1 > ^ permalink raw reply [flat|nested] 17+ messages in thread
* [PATCH 3/4] ext4: indicate via a block bitmap read is prefetched via a tracepoint 2020-07-17 15:53 [PATCH 0/4] ex4 block bitmap prefetching Theodore Ts'o 2020-07-17 15:53 ` [PATCH 1/4] ext4: add prefetching for block allocation bitmaps Theodore Ts'o 2020-07-17 15:53 ` [PATCH 2/4] ext4: skip non-loaded groups at cr=0/1 when scanning for good groups Theodore Ts'o @ 2020-07-17 15:53 ` Theodore Ts'o 2020-07-21 7:51 ` Andreas Dilger 2020-07-24 12:04 ` Благодаренко Артём 2020-07-17 15:53 ` [PATCH 4/4] ext4: add prefetch_block_bitmaps mount options Theodore Ts'o 3 siblings, 2 replies; 17+ messages in thread From: Theodore Ts'o @ 2020-07-17 15:53 UTC (permalink / raw) To: Ext4 Developers List; +Cc: Alex Zhuravlev, Theodore Ts'o Modify the ext4_read_block_bitmap_load tracepoint so that it tells us whether a block bitmap is being prefetched. Signed-off-by: Theodore Ts'o <tytso@mit.edu> --- fs/ext4/balloc.c | 2 +- include/trace/events/ext4.h | 24 ++++++++++++++++++++---- 2 files changed, 21 insertions(+), 5 deletions(-) diff --git a/fs/ext4/balloc.c b/fs/ext4/balloc.c index aaa9ec5212c8..5a2f8837200c 100644 --- a/fs/ext4/balloc.c +++ b/fs/ext4/balloc.c @@ -494,7 +494,7 @@ ext4_read_block_bitmap_nowait(struct super_block *sb, ext4_group_t block_group, * submit the buffer_head for reading */ set_buffer_new(bh); - trace_ext4_read_block_bitmap_load(sb, block_group); + trace_ext4_read_block_bitmap_load(sb, block_group, ignore_locked); bh->b_end_io = ext4_end_bitmap_read; get_bh(bh); submit_bh(REQ_OP_READ, REQ_META | REQ_PRIO | diff --git a/include/trace/events/ext4.h b/include/trace/events/ext4.h index cc41d692ae8e..cbcd2e1a608d 100644 --- a/include/trace/events/ext4.h +++ b/include/trace/events/ext4.h @@ -1312,18 +1312,34 @@ DEFINE_EVENT(ext4__bitmap_load, ext4_mb_buddy_bitmap_load, TP_ARGS(sb, group) ); -DEFINE_EVENT(ext4__bitmap_load, ext4_read_block_bitmap_load, +DEFINE_EVENT(ext4__bitmap_load, ext4_load_inode_bitmap, TP_PROTO(struct super_block *sb, unsigned long group), TP_ARGS(sb, group) ); -DEFINE_EVENT(ext4__bitmap_load, ext4_load_inode_bitmap, +TRACE_EVENT(ext4_read_block_bitmap_load, + TP_PROTO(struct super_block *sb, unsigned long group, bool prefetch), - TP_PROTO(struct super_block *sb, unsigned long group), + TP_ARGS(sb, group, prefetch), - TP_ARGS(sb, group) + TP_STRUCT__entry( + __field( dev_t, dev ) + __field( __u32, group ) + __field( bool, prefetch ) + + ), + + TP_fast_assign( + __entry->dev = sb->s_dev; + __entry->group = group; + __entry->prefetch = prefetch; + ), + + TP_printk("dev %d,%d group %u prefetch %d", + MAJOR(__entry->dev), MINOR(__entry->dev), + __entry->group, __entry->prefetch) ); TRACE_EVENT(ext4_direct_IO_enter, -- 2.24.1 ^ permalink raw reply related [flat|nested] 17+ messages in thread
* Re: [PATCH 3/4] ext4: indicate via a block bitmap read is prefetched via a tracepoint 2020-07-17 15:53 ` [PATCH 3/4] ext4: indicate via a block bitmap read is prefetched via a tracepoint Theodore Ts'o @ 2020-07-21 7:51 ` Andreas Dilger 2020-07-24 12:04 ` Благодаренко Артём 1 sibling, 0 replies; 17+ messages in thread From: Andreas Dilger @ 2020-07-21 7:51 UTC (permalink / raw) To: Theodore Ts'o; +Cc: Ext4 Developers List, Alex Zhuravlev [-- Attachment #1: Type: text/plain, Size: 2485 bytes --] On Jul 17, 2020, at 9:53 AM, Theodore Ts'o <tytso@mit.edu> wrote: > > Modify the ext4_read_block_bitmap_load tracepoint so that it tells us > whether a block bitmap is being prefetched. > > Signed-off-by: Theodore Ts'o <tytso@mit.edu> I can't really say I know much about tracepoints, but the changes look fine compared to other ext4 tracepoints. Reviewed-by: Andreas Dilger <adilger@dilger.ca> > --- > fs/ext4/balloc.c | 2 +- > include/trace/events/ext4.h | 24 ++++++++++++++++++++---- > 2 files changed, 21 insertions(+), 5 deletions(-) > > diff --git a/fs/ext4/balloc.c b/fs/ext4/balloc.c > index aaa9ec5212c8..5a2f8837200c 100644 > --- a/fs/ext4/balloc.c > +++ b/fs/ext4/balloc.c > @@ -494,7 +494,7 @@ ext4_read_block_bitmap_nowait(struct super_block *sb, ext4_group_t block_group, > * submit the buffer_head for reading > */ > set_buffer_new(bh); > - trace_ext4_read_block_bitmap_load(sb, block_group); > + trace_ext4_read_block_bitmap_load(sb, block_group, ignore_locked); > bh->b_end_io = ext4_end_bitmap_read; > get_bh(bh); > submit_bh(REQ_OP_READ, REQ_META | REQ_PRIO | > diff --git a/include/trace/events/ext4.h b/include/trace/events/ext4.h > index cc41d692ae8e..cbcd2e1a608d 100644 > --- a/include/trace/events/ext4.h > +++ b/include/trace/events/ext4.h > @@ -1312,18 +1312,34 @@ DEFINE_EVENT(ext4__bitmap_load, ext4_mb_buddy_bitmap_load, > TP_ARGS(sb, group) > ); > > -DEFINE_EVENT(ext4__bitmap_load, ext4_read_block_bitmap_load, > +DEFINE_EVENT(ext4__bitmap_load, ext4_load_inode_bitmap, > > TP_PROTO(struct super_block *sb, unsigned long group), > > TP_ARGS(sb, group) > ); > > -DEFINE_EVENT(ext4__bitmap_load, ext4_load_inode_bitmap, > +TRACE_EVENT(ext4_read_block_bitmap_load, > + TP_PROTO(struct super_block *sb, unsigned long group, bool prefetch), > > - TP_PROTO(struct super_block *sb, unsigned long group), > + TP_ARGS(sb, group, prefetch), > > - TP_ARGS(sb, group) > + TP_STRUCT__entry( > + __field( dev_t, dev ) > + __field( __u32, group ) > + __field( bool, prefetch ) > + > + ), > + > + TP_fast_assign( > + __entry->dev = sb->s_dev; > + __entry->group = group; > + __entry->prefetch = prefetch; > + ), > + > + TP_printk("dev %d,%d group %u prefetch %d", > + MAJOR(__entry->dev), MINOR(__entry->dev), > + __entry->group, __entry->prefetch) > ); > > TRACE_EVENT(ext4_direct_IO_enter, > -- > 2.24.1 > Cheers, Andreas [-- Attachment #2: Message signed with OpenPGP --] [-- Type: application/pgp-signature, Size: 873 bytes --] ^ permalink raw reply [flat|nested] 17+ messages in thread
* Re: [PATCH 3/4] ext4: indicate via a block bitmap read is prefetched via a tracepoint 2020-07-17 15:53 ` [PATCH 3/4] ext4: indicate via a block bitmap read is prefetched via a tracepoint Theodore Ts'o 2020-07-21 7:51 ` Andreas Dilger @ 2020-07-24 12:04 ` Благодаренко Артём 1 sibling, 0 replies; 17+ messages in thread From: Благодаренко Артём @ 2020-07-24 12:04 UTC (permalink / raw) To: Theodore Ts'o; +Cc: Ext4 Developers List, Alex Zhuravlev I have used this tracepoint for verifying other patches in the series. Useful. The patch looks good. Reviewed-by: Artem Blagodarenko <artem.blagodarenko@gmail.com> > On 17 Jul 2020, at 18:53, Theodore Ts'o <tytso@mit.edu> wrote: > > Modify the ext4_read_block_bitmap_load tracepoint so that it tells us > whether a block bitmap is being prefetched. > > Signed-off-by: Theodore Ts'o <tytso@mit.edu> > --- > fs/ext4/balloc.c | 2 +- > include/trace/events/ext4.h | 24 ++++++++++++++++++++---- > 2 files changed, 21 insertions(+), 5 deletions(-) > > diff --git a/fs/ext4/balloc.c b/fs/ext4/balloc.c > index aaa9ec5212c8..5a2f8837200c 100644 > --- a/fs/ext4/balloc.c > +++ b/fs/ext4/balloc.c > @@ -494,7 +494,7 @@ ext4_read_block_bitmap_nowait(struct super_block *sb, ext4_group_t block_group, > * submit the buffer_head for reading > */ > set_buffer_new(bh); > - trace_ext4_read_block_bitmap_load(sb, block_group); > + trace_ext4_read_block_bitmap_load(sb, block_group, ignore_locked); > bh->b_end_io = ext4_end_bitmap_read; > get_bh(bh); > submit_bh(REQ_OP_READ, REQ_META | REQ_PRIO | > diff --git a/include/trace/events/ext4.h b/include/trace/events/ext4.h > index cc41d692ae8e..cbcd2e1a608d 100644 > --- a/include/trace/events/ext4.h > +++ b/include/trace/events/ext4.h > @@ -1312,18 +1312,34 @@ DEFINE_EVENT(ext4__bitmap_load, ext4_mb_buddy_bitmap_load, > TP_ARGS(sb, group) > ); > > -DEFINE_EVENT(ext4__bitmap_load, ext4_read_block_bitmap_load, > +DEFINE_EVENT(ext4__bitmap_load, ext4_load_inode_bitmap, > > TP_PROTO(struct super_block *sb, unsigned long group), > > TP_ARGS(sb, group) > ); > > -DEFINE_EVENT(ext4__bitmap_load, ext4_load_inode_bitmap, > +TRACE_EVENT(ext4_read_block_bitmap_load, > + TP_PROTO(struct super_block *sb, unsigned long group, bool prefetch), > > - TP_PROTO(struct super_block *sb, unsigned long group), > + TP_ARGS(sb, group, prefetch), > > - TP_ARGS(sb, group) > + TP_STRUCT__entry( > + __field( dev_t, dev ) > + __field( __u32, group ) > + __field( bool, prefetch ) > + > + ), > + > + TP_fast_assign( > + __entry->dev = sb->s_dev; > + __entry->group = group; > + __entry->prefetch = prefetch; > + ), > + > + TP_printk("dev %d,%d group %u prefetch %d", > + MAJOR(__entry->dev), MINOR(__entry->dev), > + __entry->group, __entry->prefetch) > ); > > TRACE_EVENT(ext4_direct_IO_enter, > -- > 2.24.1 > ^ permalink raw reply [flat|nested] 17+ messages in thread
* [PATCH 4/4] ext4: add prefetch_block_bitmaps mount options 2020-07-17 15:53 [PATCH 0/4] ex4 block bitmap prefetching Theodore Ts'o ` (2 preceding siblings ...) 2020-07-17 15:53 ` [PATCH 3/4] ext4: indicate via a block bitmap read is prefetched via a tracepoint Theodore Ts'o @ 2020-07-17 15:53 ` Theodore Ts'o 2020-07-21 8:20 ` Andreas Dilger 2020-07-24 13:58 ` Благодаренко Артём 3 siblings, 2 replies; 17+ messages in thread From: Theodore Ts'o @ 2020-07-17 15:53 UTC (permalink / raw) To: Ext4 Developers List; +Cc: Alex Zhuravlev, Theodore Ts'o For file systems where we can afford to keep the buddy bitmaps cached, we can speed up initial writes to large file systems by starting to load the block allocation bitmaps as soon as the file system is mounted. This won't work well for _super_ large file systems, or memory constrained systems, so we only enable this when it is requested via a mount option. Signed-off-by: Theodore Ts'o <tytso@mit.edu> --- fs/ext4/ext4.h | 13 ++++++++++++ fs/ext4/mballoc.c | 10 ++++------ fs/ext4/super.c | 51 +++++++++++++++++++++++++++++++++++++---------- 3 files changed, 57 insertions(+), 17 deletions(-) diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h index 7451662e092a..c04d4ef0b77a 100644 --- a/fs/ext4/ext4.h +++ b/fs/ext4/ext4.h @@ -1172,6 +1172,7 @@ struct ext4_inode_info { #define EXT4_MOUNT_JOURNAL_CHECKSUM 0x800000 /* Journal checksums */ #define EXT4_MOUNT_JOURNAL_ASYNC_COMMIT 0x1000000 /* Journal Async Commit */ #define EXT4_MOUNT_WARN_ON_ERROR 0x2000000 /* Trigger WARN_ON on error */ +#define EXT4_MOUNT_PREFETCH_BLOCK_BITMAPS 0x4000000 #define EXT4_MOUNT_DELALLOC 0x8000000 /* Delalloc support */ #define EXT4_MOUNT_DATA_ERR_ABORT 0x10000000 /* Abort on file data write */ #define EXT4_MOUNT_BLOCK_VALIDITY 0x20000000 /* Block validity checking */ @@ -2315,9 +2316,15 @@ struct ext4_lazy_init { struct mutex li_list_mtx; }; +typedef enum { + EXT4_LI_MODE_ITABLE, + EXT4_LI_MODE_PREFETCH_BBITMAP +} ext4_li_mode; + struct ext4_li_request { struct super_block *lr_super; struct ext4_sb_info *lr_sbi; + ext4_li_mode lr_mode; ext4_group_t lr_next_group; struct list_head lr_request; unsigned long lr_next_sched; @@ -2657,6 +2664,12 @@ extern int ext4_mb_reserve_blocks(struct super_block *, int); extern void ext4_discard_preallocations(struct inode *); extern int __init ext4_init_mballoc(void); extern void ext4_exit_mballoc(void); +extern ext4_group_t ext4_mb_prefetch(struct super_block *sb, + ext4_group_t group, + unsigned int nr, int *cnt); +extern void ext4_mb_prefetch_fini(struct super_block *sb, ext4_group_t group, + unsigned int nr); + extern void ext4_free_blocks(handle_t *handle, struct inode *inode, struct buffer_head *bh, ext4_fsblk_t block, unsigned long count, int flags); diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c index 172994349bf6..c072d06d678d 100644 --- a/fs/ext4/mballoc.c +++ b/fs/ext4/mballoc.c @@ -2224,9 +2224,8 @@ static int ext4_mb_good_group_nolock(struct ext4_allocation_context *ac, * Start prefetching @nr block bitmaps starting at @group. * Return the next group which needs to be prefetched. */ -static ext4_group_t -ext4_mb_prefetch(struct super_block *sb, ext4_group_t group, - unsigned int nr, int *cnt) +ext4_group_t ext4_mb_prefetch(struct super_block *sb, ext4_group_t group, + unsigned int nr, int *cnt) { ext4_group_t ngroups = ext4_get_groups_count(sb); struct buffer_head *bh; @@ -2276,9 +2275,8 @@ ext4_mb_prefetch(struct super_block *sb, ext4_group_t group, * waiting for the block allocation bitmap read to finish when * ext4_mb_prefetch_fini is called from ext4_mb_regular_allocator(). */ -static void -ext4_mb_prefetch_fini(struct super_block *sb, ext4_group_t group, - unsigned int nr) +void ext4_mb_prefetch_fini(struct super_block *sb, ext4_group_t group, + unsigned int nr) { while (nr-- > 0) { struct ext4_group_desc *gdp = ext4_get_group_desc(sb, group, diff --git a/fs/ext4/super.c b/fs/ext4/super.c index 330957ed1f05..9e19d5830745 100644 --- a/fs/ext4/super.c +++ b/fs/ext4/super.c @@ -1521,6 +1521,7 @@ enum { Opt_dioread_nolock, Opt_dioread_lock, Opt_discard, Opt_nodiscard, Opt_init_itable, Opt_noinit_itable, Opt_max_dir_size_kb, Opt_nojournal_checksum, Opt_nombcache, + Opt_prefetch_block_bitmaps, }; static const match_table_t tokens = { @@ -1612,6 +1613,7 @@ static const match_table_t tokens = { {Opt_test_dummy_encryption, "test_dummy_encryption"}, {Opt_nombcache, "nombcache"}, {Opt_nombcache, "no_mbcache"}, /* for backward compatibility */ + {Opt_prefetch_block_bitmaps, "prefetch_block_bitmaps"}, {Opt_removed, "check=none"}, /* mount option from ext2/3 */ {Opt_removed, "nocheck"}, /* mount option from ext2/3 */ {Opt_removed, "reservation"}, /* mount option from ext2/3 */ @@ -1829,6 +1831,8 @@ static const struct mount_opts { {Opt_max_dir_size_kb, 0, MOPT_GTE0}, {Opt_test_dummy_encryption, 0, MOPT_STRING}, {Opt_nombcache, EXT4_MOUNT_NO_MBCACHE, MOPT_SET}, + {Opt_prefetch_block_bitmaps, EXT4_MOUNT_PREFETCH_BLOCK_BITMAPS, + MOPT_SET}, {Opt_err, 0, 0} }; @@ -3197,19 +3201,33 @@ static void print_daily_error_info(struct timer_list *t) mod_timer(&sbi->s_err_report, jiffies + 24*60*60*HZ); /* Once a day */ } +static int ext4_run_li_prefetch(struct ext4_li_request *elr, + struct super_block *sb, ext4_group_t group) +{ + unsigned int prefetch_ios = 0; + + elr->lr_next_group = ext4_mb_prefetch(sb, group, + EXT4_SB(sb)->s_mb_prefetch, + &prefetch_ios); + if (prefetch_ios) + ext4_mb_prefetch_fini(sb, elr->lr_next_group, prefetch_ios); + return (group >= elr->lr_next_group); +} + /* Find next suitable group and run ext4_init_inode_table */ static int ext4_run_li_request(struct ext4_li_request *elr) { struct ext4_group_desc *gdp = NULL; - ext4_group_t group, ngroups; - struct super_block *sb; + ext4_group_t group = elr->lr_next_group; + struct super_block *sb = elr->lr_super; + ext4_group_t ngroups = EXT4_SB(sb)->s_groups_count; unsigned long timeout = 0; int ret = 0; - sb = elr->lr_super; - ngroups = EXT4_SB(sb)->s_groups_count; + if (elr->lr_mode == EXT4_LI_MODE_PREFETCH_BBITMAP) + return ext4_run_li_prefetch(elr, sb, group); - for (group = elr->lr_next_group; group < ngroups; group++) { + for (; group < ngroups; group++) { gdp = ext4_get_group_desc(sb, group, NULL); if (!gdp) { ret = 1; @@ -3219,13 +3237,12 @@ static int ext4_run_li_request(struct ext4_li_request *elr) if (!(gdp->bg_flags & cpu_to_le16(EXT4_BG_INODE_ZEROED))) break; } - if (group >= ngroups) ret = 1; if (!ret) { timeout = jiffies; - ret = ext4_init_inode_table(sb, group, + ret = ext4_init_inode_table(elr->lr_super, group, elr->lr_timeout ? 0 : 1); if (elr->lr_timeout == 0) { timeout = (jiffies - timeout) * @@ -3234,6 +3251,10 @@ static int ext4_run_li_request(struct ext4_li_request *elr) } elr->lr_next_sched = jiffies + elr->lr_timeout; elr->lr_next_group = group + 1; + } else if (test_opt(sb, PREFETCH_BLOCK_BITMAPS)) { + elr->lr_mode = EXT4_LI_MODE_PREFETCH_BBITMAP; + elr->lr_next_group = 0; + ret = 0; } return ret; } @@ -3459,7 +3480,8 @@ static int ext4_li_info_new(void) } static struct ext4_li_request *ext4_li_request_new(struct super_block *sb, - ext4_group_t start) + ext4_group_t start, + ext4_li_mode mode) { struct ext4_sb_info *sbi = EXT4_SB(sb); struct ext4_li_request *elr; @@ -3468,6 +3490,7 @@ static struct ext4_li_request *ext4_li_request_new(struct super_block *sb, if (!elr) return NULL; + elr->lr_mode = mode; elr->lr_super = sb; elr->lr_sbi = sbi; elr->lr_next_group = start; @@ -3488,6 +3511,7 @@ int ext4_register_li_request(struct super_block *sb, struct ext4_sb_info *sbi = EXT4_SB(sb); struct ext4_li_request *elr = NULL; ext4_group_t ngroups = sbi->s_groups_count; + ext4_li_mode lr_mode = EXT4_LI_MODE_ITABLE; int ret = 0; mutex_lock(&ext4_li_mtx); @@ -3501,10 +3525,15 @@ int ext4_register_li_request(struct super_block *sb, } if (first_not_zeroed == ngroups || sb_rdonly(sb) || - !test_opt(sb, INIT_INODE_TABLE)) - goto out; + !test_opt(sb, INIT_INODE_TABLE)) { + if (test_opt(sb, PREFETCH_BLOCK_BITMAPS)) { + first_not_zeroed = 0; + lr_mode = EXT4_LI_MODE_PREFETCH_BBITMAP; + } else + goto out; + } - elr = ext4_li_request_new(sb, first_not_zeroed); + elr = ext4_li_request_new(sb, first_not_zeroed, lr_mode); if (!elr) { ret = -ENOMEM; goto out; -- 2.24.1 ^ permalink raw reply related [flat|nested] 17+ messages in thread
* Re: [PATCH 4/4] ext4: add prefetch_block_bitmaps mount options 2020-07-17 15:53 ` [PATCH 4/4] ext4: add prefetch_block_bitmaps mount options Theodore Ts'o @ 2020-07-21 8:20 ` Andreas Dilger 2020-07-24 13:58 ` Благодаренко Артём 1 sibling, 0 replies; 17+ messages in thread From: Andreas Dilger @ 2020-07-21 8:20 UTC (permalink / raw) To: Theodore Ts'o; +Cc: Ext4 Developers List, Alex Zhuravlev [-- Attachment #1: Type: text/plain, Size: 8621 bytes --] On Jul 17, 2020, at 9:53 AM, Theodore Ts'o <tytso@mit.edu> wrote: > > For file systems where we can afford to keep the buddy bitmaps cached, > we can speed up initial writes to large file systems by starting to > load the block allocation bitmaps as soon as the file system is > mounted. This won't work well for _super_ large file systems, or > memory constrained systems, so we only enable this when it is > requested via a mount option. I was looking at this, and maybe I misunderstand the code, but it looks like it does the itable zeroing first, then once that is completed it will do the block bitmap prefetch: if (first_not_zeroed == ngroups || sb_rdonly(sb) || !test_opt(sb, INIT_INODE_TABLE)) { if (test_opt(sb, PREFETCH_BLOCK_BITMAPS)) { first_not_zeroed = 0; lr_mode = EXT4_LI_MODE_PREFETCH_BBITMAP; } so it would only get into this case of first_not_zeroed == ngroups after all of the inode tables are marked zeroed in the GDT. However, it seems to me that the order of these two should be reversed, since inode table zeroing can take ages (GB/TB to write), while block bitmap loading could be done much more quickly. Also, if the itable zeroing is ever changed to verify that the itable blocks are properly marked in the block bitmap (which seems reasonable), then "prefetch" of the block bitmaps would be too late. It isn't clear if there is any benefit to also prefetch the inode bitmaps at the same time? It doesn't look like they are used by the itable zeroing code, only the GDT inode high watermark. It would seem to me that if an application is writing to a newly-mounted filesystem that the block bitmaps will *always* be needed, while itable zeroing is a "nice to have when it can be done" since there is no real expectation in the code that the itable is zeroed. Only e2fsck cares about this, and if your system fails before it finishes, you have bigger problems to worry about. I'm not adamant about changing this before landing, if you see a real benefit from this today, just some thoughts for possible improvement. Cheers, Andreas > Signed-off-by: Theodore Ts'o <tytso@mit.edu> > --- > fs/ext4/ext4.h | 13 ++++++++++++ > fs/ext4/mballoc.c | 10 ++++------ > fs/ext4/super.c | 51 +++++++++++++++++++++++++++++++++++++---------- > 3 files changed, 57 insertions(+), 17 deletions(-) > > > diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c > index 172994349bf6..c072d06d678d 100644 > --- a/fs/ext4/mballoc.c > +++ b/fs/ext4/mballoc.c > @@ -2224,9 +2224,8 @@ static int ext4_mb_good_group_nolock(struct ext4_allocation_context *ac, > * Start prefetching @nr block bitmaps starting at @group. > * Return the next group which needs to be prefetched. > */ > -static ext4_group_t > -ext4_mb_prefetch(struct super_block *sb, ext4_group_t group, > - unsigned int nr, int *cnt) > +ext4_group_t ext4_mb_prefetch(struct super_block *sb, ext4_group_t group, > + unsigned int nr, int *cnt) > { > ext4_group_t ngroups = ext4_get_groups_count(sb); > struct buffer_head *bh; > @@ -2276,9 +2275,8 @@ ext4_mb_prefetch(struct super_block *sb, ext4_group_t group, > * waiting for the block allocation bitmap read to finish when > * ext4_mb_prefetch_fini is called from ext4_mb_regular_allocator(). > */ > -static void > -ext4_mb_prefetch_fini(struct super_block *sb, ext4_group_t group, > - unsigned int nr) > +void ext4_mb_prefetch_fini(struct super_block *sb, ext4_group_t group, > + unsigned int nr) > { > while (nr-- > 0) { > struct ext4_group_desc *gdp = ext4_get_group_desc(sb, group, > diff --git a/fs/ext4/super.c b/fs/ext4/super.c > index 330957ed1f05..9e19d5830745 100644 > --- a/fs/ext4/super.c > +++ b/fs/ext4/super.c > @@ -1521,6 +1521,7 @@ enum { > Opt_dioread_nolock, Opt_dioread_lock, > Opt_discard, Opt_nodiscard, Opt_init_itable, Opt_noinit_itable, > Opt_max_dir_size_kb, Opt_nojournal_checksum, Opt_nombcache, > + Opt_prefetch_block_bitmaps, > }; > > static const match_table_t tokens = { > @@ -1612,6 +1613,7 @@ static const match_table_t tokens = { > {Opt_test_dummy_encryption, "test_dummy_encryption"}, > {Opt_nombcache, "nombcache"}, > {Opt_nombcache, "no_mbcache"}, /* for backward compatibility */ > + {Opt_prefetch_block_bitmaps, "prefetch_block_bitmaps"}, > {Opt_removed, "check=none"}, /* mount option from ext2/3 */ > {Opt_removed, "nocheck"}, /* mount option from ext2/3 */ > {Opt_removed, "reservation"}, /* mount option from ext2/3 */ > @@ -1829,6 +1831,8 @@ static const struct mount_opts { > {Opt_max_dir_size_kb, 0, MOPT_GTE0}, > {Opt_test_dummy_encryption, 0, MOPT_STRING}, > {Opt_nombcache, EXT4_MOUNT_NO_MBCACHE, MOPT_SET}, > + {Opt_prefetch_block_bitmaps, EXT4_MOUNT_PREFETCH_BLOCK_BITMAPS, > + MOPT_SET}, > {Opt_err, 0, 0} > }; > > @@ -3197,19 +3201,33 @@ static void print_daily_error_info(struct timer_list *t) > mod_timer(&sbi->s_err_report, jiffies + 24*60*60*HZ); /* Once a day */ > } > > +static int ext4_run_li_prefetch(struct ext4_li_request *elr, > + struct super_block *sb, ext4_group_t group) > +{ > + unsigned int prefetch_ios = 0; > + > + elr->lr_next_group = ext4_mb_prefetch(sb, group, > + EXT4_SB(sb)->s_mb_prefetch, > + &prefetch_ios); > + if (prefetch_ios) > + ext4_mb_prefetch_fini(sb, elr->lr_next_group, prefetch_ios); > + return (group >= elr->lr_next_group); > +} > + > /* Find next suitable group and run ext4_init_inode_table */ > static int ext4_run_li_request(struct ext4_li_request *elr) > { > struct ext4_group_desc *gdp = NULL; > - ext4_group_t group, ngroups; > - struct super_block *sb; > + ext4_group_t group = elr->lr_next_group; > + struct super_block *sb = elr->lr_super; > + ext4_group_t ngroups = EXT4_SB(sb)->s_groups_count; > unsigned long timeout = 0; > int ret = 0; > > - sb = elr->lr_super; > - ngroups = EXT4_SB(sb)->s_groups_count; > + if (elr->lr_mode == EXT4_LI_MODE_PREFETCH_BBITMAP) > + return ext4_run_li_prefetch(elr, sb, group); > > - for (group = elr->lr_next_group; group < ngroups; group++) { > + for (; group < ngroups; group++) { > gdp = ext4_get_group_desc(sb, group, NULL); > if (!gdp) { > ret = 1; > @@ -3219,13 +3237,12 @@ static int ext4_run_li_request(struct ext4_li_request *elr) > if (!(gdp->bg_flags & cpu_to_le16(EXT4_BG_INODE_ZEROED))) > break; > } > - > if (group >= ngroups) > ret = 1; > > if (!ret) { > timeout = jiffies; > - ret = ext4_init_inode_table(sb, group, > + ret = ext4_init_inode_table(elr->lr_super, group, > elr->lr_timeout ? 0 : 1); > if (elr->lr_timeout == 0) { > timeout = (jiffies - timeout) * > @@ -3234,6 +3251,10 @@ static int ext4_run_li_request(struct ext4_li_request *elr) > } > elr->lr_next_sched = jiffies + elr->lr_timeout; > elr->lr_next_group = group + 1; > + } else if (test_opt(sb, PREFETCH_BLOCK_BITMAPS)) { > + elr->lr_mode = EXT4_LI_MODE_PREFETCH_BBITMAP; > + elr->lr_next_group = 0; > + ret = 0; > } > return ret; > } > @@ -3459,7 +3480,8 @@ static int ext4_li_info_new(void) > } > > static struct ext4_li_request *ext4_li_request_new(struct super_block *sb, > - ext4_group_t start) > + ext4_group_t start, > + ext4_li_mode mode) > { > struct ext4_sb_info *sbi = EXT4_SB(sb); > struct ext4_li_request *elr; > @@ -3468,6 +3490,7 @@ static struct ext4_li_request *ext4_li_request_new(struct super_block *sb, > if (!elr) > return NULL; > > + elr->lr_mode = mode; > elr->lr_super = sb; > elr->lr_sbi = sbi; > elr->lr_next_group = start; > @@ -3488,6 +3511,7 @@ int ext4_register_li_request(struct super_block *sb, > struct ext4_sb_info *sbi = EXT4_SB(sb); > struct ext4_li_request *elr = NULL; > ext4_group_t ngroups = sbi->s_groups_count; > + ext4_li_mode lr_mode = EXT4_LI_MODE_ITABLE; > int ret = 0; > > mutex_lock(&ext4_li_mtx); > @@ -3501,10 +3525,15 @@ int ext4_register_li_request(struct super_block *sb, > } > > if (first_not_zeroed == ngroups || sb_rdonly(sb) || > - !test_opt(sb, INIT_INODE_TABLE)) > - goto out; > + !test_opt(sb, INIT_INODE_TABLE)) { > + if (test_opt(sb, PREFETCH_BLOCK_BITMAPS)) { > + first_not_zeroed = 0; > + lr_mode = EXT4_LI_MODE_PREFETCH_BBITMAP; > + } else > + goto out; > + } > > - elr = ext4_li_request_new(sb, first_not_zeroed); > + elr = ext4_li_request_new(sb, first_not_zeroed, lr_mode); > if (!elr) { > ret = -ENOMEM; > goto out; > -- > 2.24.1 > Cheers, Andreas [-- Attachment #2: Message signed with OpenPGP --] [-- Type: application/pgp-signature, Size: 873 bytes --] ^ permalink raw reply [flat|nested] 17+ messages in thread
* Re: [PATCH 4/4] ext4: add prefetch_block_bitmaps mount options 2020-07-17 15:53 ` [PATCH 4/4] ext4: add prefetch_block_bitmaps mount options Theodore Ts'o 2020-07-21 8:20 ` Andreas Dilger @ 2020-07-24 13:58 ` Благодаренко Артём 1 sibling, 0 replies; 17+ messages in thread From: Благодаренко Артём @ 2020-07-24 13:58 UTC (permalink / raw) To: Theodore Ts'o; +Cc: Ext4 Developers List, Alex Zhuravlev Hello, Thanks for patch. I believe it can be useful in some case. I have tried this patch. The option works fine. One comment is placed bellow. Best regards, Artem Blagodarenko > On 17 Jul 2020, at 18:53, Theodore Ts'o <tytso@mit.edu> wrote: > > For file systems where we can afford to keep the buddy bitmaps cached, > we can speed up initial writes to large file systems by starting to > load the block allocation bitmaps as soon as the file system is > mounted. This won't work well for _super_ large file systems, or > memory constrained systems, so we only enable this when it is > requested via a mount option. > > Signed-off-by: Theodore Ts'o <tytso@mit.edu> > --- > fs/ext4/ext4.h | 13 ++++++++++++ > fs/ext4/mballoc.c | 10 ++++------ > fs/ext4/super.c | 51 +++++++++++++++++++++++++++++++++++++---------- > 3 files changed, 57 insertions(+), 17 deletions(-) > > diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h > index 7451662e092a..c04d4ef0b77a 100644 > --- a/fs/ext4/ext4.h > +++ b/fs/ext4/ext4.h > @@ -1172,6 +1172,7 @@ struct ext4_inode_info { > #define EXT4_MOUNT_JOURNAL_CHECKSUM 0x800000 /* Journal checksums */ > #define EXT4_MOUNT_JOURNAL_ASYNC_COMMIT 0x1000000 /* Journal Async Commit */ > #define EXT4_MOUNT_WARN_ON_ERROR 0x2000000 /* Trigger WARN_ON on error */ > +#define EXT4_MOUNT_PREFETCH_BLOCK_BITMAPS 0x4000000 > #define EXT4_MOUNT_DELALLOC 0x8000000 /* Delalloc support */ > #define EXT4_MOUNT_DATA_ERR_ABORT 0x10000000 /* Abort on file data write */ > #define EXT4_MOUNT_BLOCK_VALIDITY 0x20000000 /* Block validity checking */ > @@ -2315,9 +2316,15 @@ struct ext4_lazy_init { > struct mutex li_list_mtx; > }; > > +typedef enum { > + EXT4_LI_MODE_ITABLE, > + EXT4_LI_MODE_PREFETCH_BBITMAP > +} ext4_li_mode; > + > struct ext4_li_request { > struct super_block *lr_super; > struct ext4_sb_info *lr_sbi; > + ext4_li_mode lr_mode; > ext4_group_t lr_next_group; > struct list_head lr_request; > unsigned long lr_next_sched; > @@ -2657,6 +2664,12 @@ extern int ext4_mb_reserve_blocks(struct super_block *, int); > extern void ext4_discard_preallocations(struct inode *); > extern int __init ext4_init_mballoc(void); > extern void ext4_exit_mballoc(void); > +extern ext4_group_t ext4_mb_prefetch(struct super_block *sb, > + ext4_group_t group, > + unsigned int nr, int *cnt); > +extern void ext4_mb_prefetch_fini(struct super_block *sb, ext4_group_t group, > + unsigned int nr); > + > extern void ext4_free_blocks(handle_t *handle, struct inode *inode, > struct buffer_head *bh, ext4_fsblk_t block, > unsigned long count, int flags); > diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c > index 172994349bf6..c072d06d678d 100644 > --- a/fs/ext4/mballoc.c > +++ b/fs/ext4/mballoc.c > @@ -2224,9 +2224,8 @@ static int ext4_mb_good_group_nolock(struct ext4_allocation_context *ac, > * Start prefetching @nr block bitmaps starting at @group. > * Return the next group which needs to be prefetched. > */ > -static ext4_group_t > -ext4_mb_prefetch(struct super_block *sb, ext4_group_t group, > - unsigned int nr, int *cnt) > +ext4_group_t ext4_mb_prefetch(struct super_block *sb, ext4_group_t group, > + unsigned int nr, int *cnt) > { > ext4_group_t ngroups = ext4_get_groups_count(sb); > struct buffer_head *bh; > @@ -2276,9 +2275,8 @@ ext4_mb_prefetch(struct super_block *sb, ext4_group_t group, > * waiting for the block allocation bitmap read to finish when > * ext4_mb_prefetch_fini is called from ext4_mb_regular_allocator(). > */ > -static void > -ext4_mb_prefetch_fini(struct super_block *sb, ext4_group_t group, > - unsigned int nr) > +void ext4_mb_prefetch_fini(struct super_block *sb, ext4_group_t group, > + unsigned int nr) > { > while (nr-- > 0) { > struct ext4_group_desc *gdp = ext4_get_group_desc(sb, group, > diff --git a/fs/ext4/super.c b/fs/ext4/super.c > index 330957ed1f05..9e19d5830745 100644 > --- a/fs/ext4/super.c > +++ b/fs/ext4/super.c > @@ -1521,6 +1521,7 @@ enum { > Opt_dioread_nolock, Opt_dioread_lock, > Opt_discard, Opt_nodiscard, Opt_init_itable, Opt_noinit_itable, > Opt_max_dir_size_kb, Opt_nojournal_checksum, Opt_nombcache, > + Opt_prefetch_block_bitmaps, > }; > > static const match_table_t tokens = { > @@ -1612,6 +1613,7 @@ static const match_table_t tokens = { > {Opt_test_dummy_encryption, "test_dummy_encryption"}, > {Opt_nombcache, "nombcache"}, > {Opt_nombcache, "no_mbcache"}, /* for backward compatibility */ > + {Opt_prefetch_block_bitmaps, "prefetch_block_bitmaps"}, > {Opt_removed, "check=none"}, /* mount option from ext2/3 */ > {Opt_removed, "nocheck"}, /* mount option from ext2/3 */ > {Opt_removed, "reservation"}, /* mount option from ext2/3 */ > @@ -1829,6 +1831,8 @@ static const struct mount_opts { > {Opt_max_dir_size_kb, 0, MOPT_GTE0}, > {Opt_test_dummy_encryption, 0, MOPT_STRING}, > {Opt_nombcache, EXT4_MOUNT_NO_MBCACHE, MOPT_SET}, > + {Opt_prefetch_block_bitmaps, EXT4_MOUNT_PREFETCH_BLOCK_BITMAPS, > + MOPT_SET}, > {Opt_err, 0, 0} > }; > > @@ -3197,19 +3201,33 @@ static void print_daily_error_info(struct timer_list *t) > mod_timer(&sbi->s_err_report, jiffies + 24*60*60*HZ); /* Once a day */ > } > > +static int ext4_run_li_prefetch(struct ext4_li_request *elr, > + struct super_block *sb, ext4_group_t group) > +{ > + unsigned int prefetch_ios = 0; > + > + elr->lr_next_group = ext4_mb_prefetch(sb, group, > + EXT4_SB(sb)->s_mb_prefetch, > + &prefetch_ios); > + if (prefetch_ios) > + ext4_mb_prefetch_fini(sb, elr->lr_next_group, prefetch_ios); > + return (group >= elr->lr_next_group); > +} > + > /* Find next suitable group and run ext4_init_inode_table */ > static int ext4_run_li_request(struct ext4_li_request *elr) > { > struct ext4_group_desc *gdp = NULL; > - ext4_group_t group, ngroups; > - struct super_block *sb; > + ext4_group_t group = elr->lr_next_group; > + struct super_block *sb = elr->lr_super; > + ext4_group_t ngroups = EXT4_SB(sb)->s_groups_count; > unsigned long timeout = 0; > int ret = 0; > > - sb = elr->lr_super; > - ngroups = EXT4_SB(sb)->s_groups_count; > + if (elr->lr_mode == EXT4_LI_MODE_PREFETCH_BBITMAP) > + return ext4_run_li_prefetch(elr, sb, group); > > - for (group = elr->lr_next_group; group < ngroups; group++) { > + for (; group < ngroups; group++) { > gdp = ext4_get_group_desc(sb, group, NULL); > if (!gdp) { > ret = 1; > @@ -3219,13 +3237,12 @@ static int ext4_run_li_request(struct ext4_li_request *elr) > if (!(gdp->bg_flags & cpu_to_le16(EXT4_BG_INODE_ZEROED))) > break; > } > - > if (group >= ngroups) > ret = 1; > > if (!ret) { > timeout = jiffies; > - ret = ext4_init_inode_table(sb, group, > + ret = ext4_init_inode_table(elr->lr_super, group, > elr->lr_timeout ? 0 : 1); > if (elr->lr_timeout == 0) { > timeout = (jiffies - timeout) * > @@ -3234,6 +3251,10 @@ static int ext4_run_li_request(struct ext4_li_request *elr) > } > elr->lr_next_sched = jiffies + elr->lr_timeout; > elr->lr_next_group = group + 1; > + } else if (test_opt(sb, PREFETCH_BLOCK_BITMAPS)) { > + elr->lr_mode = EXT4_LI_MODE_PREFETCH_BBITMAP; > + elr->lr_next_group = 0; > + ret = 0; > } > return ret; > } > @@ -3459,7 +3480,8 @@ static int ext4_li_info_new(void) > } > > static struct ext4_li_request *ext4_li_request_new(struct super_block *sb, > - ext4_group_t start) > + ext4_group_t start, > + ext4_li_mode mode) > { > struct ext4_sb_info *sbi = EXT4_SB(sb); > struct ext4_li_request *elr; > @@ -3468,6 +3490,7 @@ static struct ext4_li_request *ext4_li_request_new(struct super_block *sb, > if (!elr) > return NULL; > > + elr->lr_mode = mode; > elr->lr_super = sb; > elr->lr_sbi = sbi; > elr->lr_next_group = start; > @@ -3488,6 +3511,7 @@ int ext4_register_li_request(struct super_block *sb, > struct ext4_sb_info *sbi = EXT4_SB(sb); > struct ext4_li_request *elr = NULL; > ext4_group_t ngroups = sbi->s_groups_count; > + ext4_li_mode lr_mode = EXT4_LI_MODE_ITABLE; > int ret = 0; > > mutex_lock(&ext4_li_mtx); > @@ -3501,10 +3525,15 @@ int ext4_register_li_request(struct super_block *sb, > } > > if (first_not_zeroed == ngroups || sb_rdonly(sb) || > - !test_opt(sb, INIT_INODE_TABLE)) > - goto out; > + !test_opt(sb, INIT_INODE_TABLE)) { > + if (test_opt(sb, PREFETCH_BLOCK_BITMAPS)) { > + first_not_zeroed = 0; ext4_register_li_request() can be called on EXT4_IOC_RESIZE_FS lctl as err = ext4_register_li_request(sb, o_group); In this case inode tables will be initialised started from new block range, but block bitmaps loading loop will start from group 0. Yes, this loaded groups will be skipped finally, but there are useless CPU time. > + lr_mode = EXT4_LI_MODE_PREFETCH_BBITMAP; > + } else > + goto out; > + } > > - elr = ext4_li_request_new(sb, first_not_zeroed); > + elr = ext4_li_request_new(sb, first_not_zeroed, lr_mode); > if (!elr) { > ret = -ENOMEM; > goto out; > -- > 2.24.1 > ^ permalink raw reply [flat|nested] 17+ messages in thread
* [PATCH 0/4] V2- ext4 block bitmap prefetch patches @ 2020-07-31 19:08 Theodore Ts'o 2020-07-31 19:08 ` [PATCH 2/4] ext4: skip non-loaded groups at cr=0/1 when scanning for good groups Theodore Ts'o 0 siblings, 1 reply; 17+ messages in thread From: Theodore Ts'o @ 2020-07-31 19:08 UTC (permalink / raw) To: Ext4 Developers List; +Cc: Theodore Ts'o This is a second revision of Alex's original block allocation prefetch patches. Changes are from v1: *) We don't skip reading block bitmaps in the first block group of a flex_bg. This is necessary so that strategy of biasing block allocations for metadata blocks (in particular, extent tree blocks) can be preserved. *) The prefetch_block_bitmaps mount option now will prefetch the block bitmaps before starting lazy inode table initialization, instead of the other way around. In general, for freshly created file systems, prefetching block bitmaps will go very quickly, since most block groups have not been used yet, so we don't actually the prefetch those block bitmaps. *) Other minor spelling fixups, cleanups. Alex Zhuravlev (2): ext4: add prefetching for block allocation bitmaps ext4: skip non-loaded groups at cr=0/1 when scanning for good groups Theodore Ts'o (2): ext4: indicate via a block bitmap read is prefetched via a tracepoint ext4: add prefetch_block_bitmaps mount options fs/ext4/balloc.c | 16 +++- fs/ext4/ext4.h | 23 +++++- fs/ext4/mballoc.c | 153 +++++++++++++++++++++++++++++++++++- fs/ext4/super.c | 59 ++++++++++---- fs/ext4/sysfs.c | 4 + include/trace/events/ext4.h | 68 +++++++++++++++- 6 files changed, 294 insertions(+), 29 deletions(-) -- 2.24.1 ^ permalink raw reply [flat|nested] 17+ messages in thread
* [PATCH 2/4] ext4: skip non-loaded groups at cr=0/1 when scanning for good groups 2020-07-31 19:08 [PATCH 0/4] V2- ext4 block bitmap prefetch patches Theodore Ts'o @ 2020-07-31 19:08 ` Theodore Ts'o 2020-08-01 8:49 ` Andreas Dilger 0 siblings, 1 reply; 17+ messages in thread From: Theodore Ts'o @ 2020-07-31 19:08 UTC (permalink / raw) To: Ext4 Developers List; +Cc: Alex Zhuravlev, Andreas Dilger, Artem Blagodarenko From: Alex Zhuravlev <azhuravlev@whamcloud.com> cr=0 is supposed to be an optimization to save CPU cycles, but if buddy data (in memory) is not initialized then all this makes no sense as we have to do sync IO taking a lot of cycles. Also, at cr=0 mballoc doesn't choose any avaibale chunk. cr=1 also skips groups using heuristic based on avg. fragment size. It's more useful to skip such groups and switch to cr=2 where groups will be scanned for available chunks. However, we always read the first block group in a flex_bg so metadata blocks will get read into the first flex_bg if possible. Using sparse image and dm-slow virtual device of 120TB was simulated, then the image was formatted and filled using debugfs to mark ~85% of available space as busy. mount process w/o the patch couldn't complete in half an hour (according to vmstat it would take ~10-11 hours). With the patch applied mount took ~20 seconds. Lustre-bug-id: https://jira.whamcloud.com/browse/LU-12988 Signed-off-by: Alex Zhuravlev <azhuravlev@whamcloud.com> Reviewed-by: Andreas Dilger <adilger@whamcloud.com> Reviewed-by: Artem Blagodarenko <artem.blagodarenko@gmail.com> --- fs/ext4/mballoc.c | 22 +++++++++++++++++++++- 1 file changed, 21 insertions(+), 1 deletion(-) diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c index fcc702f1ff15..b1ef35a9e9f1 100644 --- a/fs/ext4/mballoc.c +++ b/fs/ext4/mballoc.c @@ -2177,6 +2177,7 @@ static int ext4_mb_good_group_nolock(struct ext4_allocation_context *ac, { struct ext4_group_info *grp = ext4_get_group_info(ac->ac_sb, group); struct super_block *sb = ac->ac_sb; + struct ext4_sb_info *sbi = EXT4_SB(sb); bool should_lock = ac->ac_flags & EXT4_MB_STRICT_CHECK; ext4_grpblk_t free; int ret = 0; @@ -2195,7 +2196,26 @@ static int ext4_mb_good_group_nolock(struct ext4_allocation_context *ac, /* We only do this if the grp has never been initialized */ if (unlikely(EXT4_MB_GRP_NEED_INIT(grp))) { - ret = ext4_mb_init_group(ac->ac_sb, group, GFP_NOFS); + struct ext4_group_desc *gdp = + ext4_get_group_desc(sb, group, NULL); + int ret; + + /* cr=0/1 is a very optimistic search to find large + * good chunks almost for free. If buddy data is not + * ready, then this optimization makes no sense. But + * we never skip the first block group in a flex_bg, + * since this gets used for metadata block allocation, + * and we want to make sure we locate metadata blocks + * in the first block group in the flex_bg if + * possible. + */ + if (cr < 2 && + (!sbi->s_log_groups_per_flex || + ((group & ((1 << sbi->s_log_groups_per_flex) - 1)) != 0)) && + !(ext4_has_group_desc_csum(sb) && + (gdp->bg_flags & cpu_to_le16(EXT4_BG_BLOCK_UNINIT)))) + return 0; + ret = ext4_mb_init_group(sb, group, GFP_NOFS); if (ret) return ret; } -- 2.24.1 ^ permalink raw reply related [flat|nested] 17+ messages in thread
* Re: [PATCH 2/4] ext4: skip non-loaded groups at cr=0/1 when scanning for good groups 2020-07-31 19:08 ` [PATCH 2/4] ext4: skip non-loaded groups at cr=0/1 when scanning for good groups Theodore Ts'o @ 2020-08-01 8:49 ` Andreas Dilger 0 siblings, 0 replies; 17+ messages in thread From: Andreas Dilger @ 2020-08-01 8:49 UTC (permalink / raw) To: Theodore Ts'o Cc: Ext4 Developers List, Alex Zhuravlev, Artem Blagodarenko [-- Attachment #1: Type: text/plain, Size: 2936 bytes --] > On Jul 31, 2020, at 1:08 PM, Theodore Ts'o <tytso@mit.edu> wrote: > > From: Alex Zhuravlev <azhuravlev@whamcloud.com> > > cr=0 is supposed to be an optimization to save CPU cycles, but if > buddy data (in memory) is not initialized then all this makes no sense > as we have to do sync IO taking a lot of cycles. Also, at cr=0 > mballoc doesn't choose any avaibale chunk. cr=1 also skips groups (typo) "available" > using heuristic based on avg. fragment size. It's more useful to skip > such groups and switch to cr=2 where groups will be scanned for > available chunks. However, we always read the first block group in a > flex_bg so metadata blocks will get read into the first flex_bg if > possible. > > Using sparse image and dm-slow virtual device of 120TB was > simulated, then the image was formatted and filled using debugfs to > mark ~85% of available space as busy. mount process w/o the patch > couldn't complete in half an hour (according to vmstat it would take > ~10-11 hours). With the patch applied mount took ~20 seconds. > > Lustre-bug-id: https://jira.whamcloud.com/browse/LU-12988 > Signed-off-by: Alex Zhuravlev <azhuravlev@whamcloud.com> > Reviewed-by: Andreas Dilger <adilger@whamcloud.com> > Reviewed-by: Artem Blagodarenko <artem.blagodarenko@gmail.com> Looks good, one trivial cleanup below could also be done before landing. > --- > fs/ext4/mballoc.c | 22 +++++++++++++++++++++- > 1 file changed, 21 insertions(+), 1 deletion(-) > > diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c > index fcc702f1ff15..b1ef35a9e9f1 100644 > --- a/fs/ext4/mballoc.c > +++ b/fs/ext4/mballoc.c > @@ -2195,7 +2196,26 @@ static int ext4_mb_good_group_nolock(struct ext4_allocation_context *ac, > > /* We only do this if the grp has never been initialized */ > if (unlikely(EXT4_MB_GRP_NEED_INIT(grp))) { > - ret = ext4_mb_init_group(ac->ac_sb, group, GFP_NOFS); > + struct ext4_group_desc *gdp = > + ext4_get_group_desc(sb, group, NULL); > + int ret; > + > + /* cr=0/1 is a very optimistic search to find large > + * good chunks almost for free. If buddy data is not > + * ready, then this optimization makes no sense. But > + * we never skip the first block group in a flex_bg, > + * since this gets used for metadata block allocation, > + * and we want to make sure we locate metadata blocks > + * in the first block group in the flex_bg if > + * possible. (style) "possible" could fit on the previous line? > + */ > + if (cr < 2 && > + (!sbi->s_log_groups_per_flex || > + ((group & ((1 << sbi->s_log_groups_per_flex) - 1)) != 0)) && > + !(ext4_has_group_desc_csum(sb) && > + (gdp->bg_flags & cpu_to_le16(EXT4_BG_BLOCK_UNINIT)))) > + return 0; > + ret = ext4_mb_init_group(sb, group, GFP_NOFS); > if (ret) > return ret; > } > -- > 2.24.1 > Cheers, Andreas [-- Attachment #2: Message signed with OpenPGP --] [-- Type: application/pgp-signature, Size: 873 bytes --] ^ permalink raw reply [flat|nested] 17+ messages in thread
end of thread, other threads:[~2020-08-01 8:49 UTC | newest] Thread overview: 17+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2020-07-17 15:53 [PATCH 0/4] ex4 block bitmap prefetching Theodore Ts'o 2020-07-17 15:53 ` [PATCH 1/4] ext4: add prefetching for block allocation bitmaps Theodore Ts'o 2020-07-17 21:55 ` kernel test robot 2020-07-21 7:42 ` Andreas Dilger 2020-07-23 0:36 ` Shuichi Ihara 2020-07-23 15:00 ` tytso 2020-07-17 15:53 ` [PATCH 2/4] ext4: skip non-loaded groups at cr=0/1 when scanning for good groups Theodore Ts'o 2020-07-21 7:48 ` Andreas Dilger 2020-07-24 11:27 ` Благодаренко Артём 2020-07-17 15:53 ` [PATCH 3/4] ext4: indicate via a block bitmap read is prefetched via a tracepoint Theodore Ts'o 2020-07-21 7:51 ` Andreas Dilger 2020-07-24 12:04 ` Благодаренко Артём 2020-07-17 15:53 ` [PATCH 4/4] ext4: add prefetch_block_bitmaps mount options Theodore Ts'o 2020-07-21 8:20 ` Andreas Dilger 2020-07-24 13:58 ` Благодаренко Артём 2020-07-31 19:08 [PATCH 0/4] V2- ext4 block bitmap prefetch patches Theodore Ts'o 2020-07-31 19:08 ` [PATCH 2/4] ext4: skip non-loaded groups at cr=0/1 when scanning for good groups Theodore Ts'o 2020-08-01 8:49 ` Andreas Dilger
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