From: Qu Wenruo <quwenruo.btrfs@gmx.com>
To: Josef Bacik <josef@toxicpanda.com>, Qu Wenruo <wqu@suse.com>,
linux-btrfs@vger.kernel.org
Subject: Re: [PATCH v4 17/18] btrfs: integrate page status update for data read path into begin/end_page_read()
Date: Thu, 21 Jan 2021 09:05:57 +0800 [thread overview]
Message-ID: <490e331e-a586-3e7a-db59-b360a8118a50@gmx.com> (raw)
In-Reply-To: <b5e21d24-d2db-dc0f-bd96-1cbcad1a634e@toxicpanda.com>
On 2021/1/20 下午11:41, Josef Bacik wrote:
> On 1/16/21 2:15 AM, Qu Wenruo wrote:
>> In btrfs data page read path, the page status update are handled in two
>> different locations:
>>
>> btrfs_do_read_page()
>> {
>> while (cur <= end) {
>> /* No need to read from disk */
>> if (HOLE/PREALLOC/INLINE){
>> memset();
>> set_extent_uptodate();
>> continue;
>> }
>> /* Read from disk */
>> ret = submit_extent_page(end_bio_extent_readpage);
>> }
>>
>> end_bio_extent_readpage()
>> {
>> endio_readpage_uptodate_page_status();
>> }
>>
>> This is fine for sectorsize == PAGE_SIZE case, as for above loop we
>> should only hit one branch and then exit.
>>
>> But for subpage, there are more works to be done in page status update:
>> - Page Unlock condition
>> Unlike regular page size == sectorsize case, we can no longer just
>> unlock a page without a brain.
>> Only the last reader of the page can unlock the page.
>> This means, we can unlock the page either in the while() loop, or in
>> the endio function.
>>
>> - Page uptodate condition
>> Since we have multiple sectors to read for a page, we can only mark
>> the full page uptodate if all sectors are uptodate.
>>
>> To handle both subpage and regular cases, introduce a pair of functions
>> to help handling page status update:
>>
>> - being_page_read()
>> For regular case, it does nothing.
>> For subpage case, it update the reader counters so that later
>> end_page_read() can know who is the last one to unlock the page.
>>
>> - end_page_read()
>> This is just endio_readpage_uptodate_page_status() renamed.
>> The original name is a little too long and too specific for endio.
>>
>> The only new trick added is the condition for page unlock.
>> Now for subage data, we unlock the page if we're the last reader.
>>
>> This does not only provide the basis for subpage data read, but also
>> hide the special handling of page read from the main read loop.
>>
>> Signed-off-by: Qu Wenruo <wqu@suse.com>
>> ---
>> fs/btrfs/extent_io.c | 38 +++++++++++++++++++----------
>> fs/btrfs/subpage.h | 57 +++++++++++++++++++++++++++++++++++---------
>> 2 files changed, 72 insertions(+), 23 deletions(-)
>>
>> diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
>> index 4bce03fed205..6ae820144ec7 100644
>> --- a/fs/btrfs/extent_io.c
>> +++ b/fs/btrfs/extent_io.c
>> @@ -2839,8 +2839,17 @@ static void
>> endio_readpage_release_extent(struct processed_extent *processed,
>> processed->uptodate = uptodate;
>> }
>> -static void endio_readpage_update_page_status(struct page *page, bool
>> uptodate,
>> - u64 start, u32 len)
>> +static void begin_data_page_read(struct btrfs_fs_info *fs_info,
>> struct page *page)
>> +{
>> + ASSERT(PageLocked(page));
>> + if (fs_info->sectorsize == PAGE_SIZE)
>> + return;
>> +
>> + ASSERT(PagePrivate(page));
>> + btrfs_subpage_start_reader(fs_info, page, page_offset(page),
>> PAGE_SIZE);
>> +}
>> +
>> +static void end_page_read(struct page *page, bool uptodate, u64
>> start, u32 len)
>> {
>> struct btrfs_fs_info *fs_info =
>> btrfs_sb(page->mapping->host->i_sb);
>> @@ -2856,7 +2865,12 @@ static void
>> endio_readpage_update_page_status(struct page *page, bool uptodate,
>> if (fs_info->sectorsize == PAGE_SIZE)
>> unlock_page(page);
>> - /* Subpage locking will be handled in later patches */
>> + else if (is_data_inode(page->mapping->host))
>> + /*
>> + * For subpage data, unlock the page if we're the last reader.
>> + * For subpage metadata, page lock is not utilized for read.
>> + */
>> + btrfs_subpage_end_reader(fs_info, page, start, len);
>> }
>> /*
>> @@ -2993,7 +3007,7 @@ static void end_bio_extent_readpage(struct bio
>> *bio)
>> bio_offset += len;
>> /* Update page status and unlock */
>> - endio_readpage_update_page_status(page, uptodate, start, len);
>> + end_page_read(page, uptodate, start, len);
>> endio_readpage_release_extent(&processed, BTRFS_I(inode),
>> start, end, uptodate);
>> }
>> @@ -3267,6 +3281,7 @@ int btrfs_do_readpage(struct page *page, struct
>> extent_map **em_cached,
>> unsigned int read_flags, u64 *prev_em_start)
>> {
>> struct inode *inode = page->mapping->host;
>> + struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
>> u64 start = page_offset(page);
>> const u64 end = start + PAGE_SIZE - 1;
>> u64 cur = start;
>> @@ -3310,6 +3325,7 @@ int btrfs_do_readpage(struct page *page, struct
>> extent_map **em_cached,
>> kunmap_atomic(userpage);
>> }
>> }
>> + begin_data_page_read(fs_info, page);
>> while (cur <= end) {
>> bool force_bio_submit = false;
>> u64 disk_bytenr;
>> @@ -3327,13 +3343,14 @@ int btrfs_do_readpage(struct page *page,
>> struct extent_map **em_cached,
>> &cached, GFP_NOFS);
>> unlock_extent_cached(tree, cur,
>> cur + iosize - 1, &cached);
>> + end_page_read(page, true, cur, iosize);
>> break;
>> }
>> em = __get_extent_map(inode, page, pg_offset, cur,
>> end - cur + 1, em_cached);
>> if (IS_ERR_OR_NULL(em)) {
>> - SetPageError(page);
>> unlock_extent(tree, cur, end);
>> + end_page_read(page, false, cur, end + 1 - cur);
>> break;
>> }
>> extent_offset = cur - em->start;
>> @@ -3416,6 +3433,7 @@ int btrfs_do_readpage(struct page *page, struct
>> extent_map **em_cached,
>> &cached, GFP_NOFS);
>> unlock_extent_cached(tree, cur,
>> cur + iosize - 1, &cached);
>> + end_page_read(page, true, cur, iosize);
>> cur = cur + iosize;
>> pg_offset += iosize;
>> continue;
>> @@ -3425,6 +3443,7 @@ int btrfs_do_readpage(struct page *page, struct
>> extent_map **em_cached,
>> EXTENT_UPTODATE, 1, NULL)) {
>> check_page_uptodate(tree, page);
>> unlock_extent(tree, cur, cur + iosize - 1);
>> + end_page_read(page, true, cur, iosize);
>> cur = cur + iosize;
>> pg_offset += iosize;
>> continue;
>> @@ -3433,8 +3452,8 @@ int btrfs_do_readpage(struct page *page, struct
>> extent_map **em_cached,
>> * to date. Error out
>> */
>> if (block_start == EXTENT_MAP_INLINE) {
>> - SetPageError(page);
>> unlock_extent(tree, cur, cur + iosize - 1);
>> + end_page_read(page, false, cur, iosize);
>> cur = cur + iosize;
>> pg_offset += iosize;
>> continue;
>> @@ -3451,19 +3470,14 @@ int btrfs_do_readpage(struct page *page,
>> struct extent_map **em_cached,
>> nr++;
>> *bio_flags = this_bio_flag;
>> } else {
>> - SetPageError(page);
>> unlock_extent(tree, cur, cur + iosize - 1);
>> + end_page_read(page, false, cur, iosize);
>> goto out;
>> }
>> cur = cur + iosize;
>> pg_offset += iosize;
>> }
>> out:
>> - if (!nr) {
>> - if (!PageError(page))
>> - SetPageUptodate(page);
>> - unlock_page(page);
>> - }
>
> Huh? Now in the normal case we're not getting an unlocked page.
The page unlock is handled in end_page_read().
We need no special handling at all now, everything is handled in each
branch, thus at the end, we have nothing to bother.
> Not
> only that we're not setting it uptodate if we had to 0 the whole page,
> so we're just left dangling here because the endio will never be called.
Page read only have two routines: go submit bio to do the read, or fill
it with zero inside btrfs_do_readpage() right now.
Now in btrfs_do_readpage(), we call end_page_read() in all branches
except the bio submittion route.
So every bytes would be covered.
This is especially important for subpage, e.g:
For a 64K which has two extents in it:
0 32K 64K
|---- Hole -----|--- Regular ---|
In this case, we fill zero for [0, 32K), set it uptodate in
end_read_page(), reduce readers to 8 but not unlock the page, generate a
bio for [32K, 64K).
And in endio for [32K, 64) we will set the range uptodate, and the full
page uptodate, reduce readers to 0, and unlock the page.
For regular sectorsize, it's either a hole or a regular, we always
unlock the page, set uptodate or err in end_page_read().
>
> Not to mention you're deleting all of teh SetPageError() calls for no
> reason that I can see, and not replacing it with anything else, so
> you've essentially ripped out any error handling on memory allocation.
Nope, just check end_page_read(), if @uptodate is false, we set the page
range error.
I guess you need to read the code not using difftool, but in code,
epseiclaly in 0014 I integrated the page lock/unlock into
endio_readpage_uptodate_page_status(), which later becomes end_page_read().
And if it's really as you said, I miss page unlock, very basic fsstress
can exposed it on x86, not to mention full fstests.
Thanks,
Qu
> Thanks,
>
> Josef
next prev parent reply other threads:[~2021-01-21 1:08 UTC|newest]
Thread overview: 68+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-16 7:15 [PATCH v4 00/18] btrfs: add read-only support for subpage sector size Qu Wenruo
2021-01-16 7:15 ` [PATCH v4 01/18] btrfs: update locked page dirty/writeback/error bits in __process_pages_contig() Qu Wenruo
2021-01-19 21:41 ` Josef Bacik
2021-01-21 6:32 ` Qu Wenruo
2021-01-21 6:51 ` Qu Wenruo
2021-01-23 19:13 ` David Sterba
2021-01-24 0:35 ` Qu Wenruo
2021-01-24 11:49 ` David Sterba
2021-01-16 7:15 ` [PATCH v4 02/18] btrfs: merge PAGE_CLEAR_DIRTY and PAGE_SET_WRITEBACK into PAGE_START_WRITEBACK Qu Wenruo
2021-01-19 21:43 ` Josef Bacik
2021-01-19 21:45 ` Josef Bacik
2021-01-16 7:15 ` [PATCH v4 03/18] btrfs: introduce the skeleton of btrfs_subpage structure Qu Wenruo
2021-01-18 22:46 ` David Sterba
2021-01-18 22:54 ` Qu Wenruo
2021-01-19 15:51 ` David Sterba
2021-01-19 16:06 ` David Sterba
2021-01-20 0:19 ` Qu Wenruo
2021-01-23 19:37 ` David Sterba
2021-01-24 0:24 ` Qu Wenruo
2021-01-18 23:01 ` David Sterba
2021-01-16 7:15 ` [PATCH v4 04/18] btrfs: make attach_extent_buffer_page() to handle subpage case Qu Wenruo
2021-01-18 22:51 ` David Sterba
2021-01-19 21:54 ` Josef Bacik
2021-01-19 22:35 ` David Sterba
2021-01-26 7:29 ` Qu Wenruo
2021-01-27 19:58 ` David Sterba
2021-01-20 0:27 ` Qu Wenruo
2021-01-20 14:22 ` Josef Bacik
2021-01-21 1:20 ` Qu Wenruo
2021-01-16 7:15 ` [PATCH v4 05/18] btrfs: make grab_extent_buffer_from_page() " Qu Wenruo
2021-01-16 7:15 ` [PATCH v4 06/18] btrfs: support subpage for extent buffer page release Qu Wenruo
2021-01-20 14:44 ` Josef Bacik
2021-01-21 0:45 ` Qu Wenruo
2021-01-16 7:15 ` [PATCH v4 07/18] btrfs: attach private to dummy extent buffer pages Qu Wenruo
2021-01-20 14:48 ` Josef Bacik
2021-01-21 0:47 ` Qu Wenruo
2021-01-16 7:15 ` [PATCH v4 08/18] btrfs: introduce helper for subpage uptodate status Qu Wenruo
2021-01-19 19:45 ` David Sterba
2021-01-20 14:55 ` Josef Bacik
2021-01-26 7:21 ` Qu Wenruo
2021-01-20 15:00 ` Josef Bacik
2021-01-21 0:49 ` Qu Wenruo
2021-01-21 1:28 ` Josef Bacik
2021-01-21 1:38 ` Qu Wenruo
2021-01-16 7:15 ` [PATCH v4 09/18] btrfs: introduce helper for subpage error status Qu Wenruo
2021-01-16 7:15 ` [PATCH v4 10/18] btrfs: make set/clear_extent_buffer_uptodate() to support subpage size Qu Wenruo
2021-01-16 7:15 ` [PATCH v4 11/18] btrfs: make btrfs_clone_extent_buffer() to be subpage compatible Qu Wenruo
2021-01-16 7:15 ` [PATCH v4 12/18] btrfs: implement try_release_extent_buffer() for subpage metadata support Qu Wenruo
2021-01-20 15:05 ` Josef Bacik
2021-01-21 0:51 ` Qu Wenruo
2021-01-23 20:36 ` David Sterba
2021-01-25 20:02 ` Josef Bacik
2021-01-16 7:15 ` [PATCH v4 13/18] btrfs: introduce read_extent_buffer_subpage() Qu Wenruo
2021-01-20 15:08 ` Josef Bacik
2021-01-16 7:15 ` [PATCH v4 14/18] btrfs: extent_io: make endio_readpage_update_page_status() to handle subpage case Qu Wenruo
2021-01-16 7:15 ` [PATCH v4 15/18] btrfs: disk-io: introduce subpage metadata validation check Qu Wenruo
2021-01-16 7:15 ` [PATCH v4 16/18] btrfs: introduce btrfs_subpage for data inodes Qu Wenruo
2021-01-19 20:48 ` David Sterba
2021-01-20 15:28 ` Josef Bacik
2021-01-26 7:05 ` Qu Wenruo
2021-01-16 7:15 ` [PATCH v4 17/18] btrfs: integrate page status update for data read path into begin/end_page_read() Qu Wenruo
2021-01-20 15:41 ` Josef Bacik
2021-01-21 1:05 ` Qu Wenruo [this message]
2021-01-16 7:15 ` [PATCH v4 18/18] btrfs: allow RO mount of 4K sector size fs on 64K page system Qu Wenruo
2021-01-18 23:17 ` [PATCH v4 00/18] btrfs: add read-only support for subpage sector size David Sterba
2021-01-18 23:26 ` Qu Wenruo
2021-01-24 12:29 ` David Sterba
2021-01-25 1:19 ` Qu Wenruo
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