* [PATCH] zswap: Zero-filled pages handling [not found] <CGME20170225144222epcms5p15930f37372ec628420474e4d43ccfa16@epcms5p1> @ 2017-02-25 14:42 ` Srividya Desireddy 2017-02-25 17:18 ` Sarbojit Ganguly 0 siblings, 1 reply; 5+ messages in thread From: Srividya Desireddy @ 2017-02-25 14:42 UTC (permalink / raw) To: sjenning, ddstreet, penberg, linux-mm, linux-kernel Cc: Dinakar Reddy Pathireddy, SHARAN ALLUR, SUNEEL KUMAR SURIMANI, JUHUN KIM, srividya.desireddy, Sarbojit Ganguly [-- Attachment #1: Type: text/plain, Size: 5577 bytes --] From: Srividya Desireddy <srividya.dr@samsung.com> Date: Thu, 23 Feb 2017 15:04:06 +0530 Subject: [PATCH] zswap: Zero-filled pages handling Zswap is a cache which compresses the pages that are being swapped out and stores them into a dynamically allocated RAM-based memory pool. Experiments have shown that around 10-20% of pages stored in zswap are zero-filled pages (i.e. contents of the page are all zeros), but these pages are handled as normal pages by compressing and allocating memory in the pool. This patch adds a check in zswap_frontswap_store() to identify zero-filled page before compression of the page. If the page is a zero-filled page, set zswap_entry.zeroflag and skip the compression of the page and alloction of memory in zpool. In zswap_frontswap_load(), check if the zeroflag is set for the page in zswap_entry. If the flag is set, memset the page with zero. This saves the decompression time during load. The overall overhead caused to check for a zero-filled page is very minimal when compared to the time saved by avoiding compression and allocation in case of zero-filled pages. Although, compressed size of a zero-filled page is very less, with this patch load time of a zero-filled page is reduced by 80% when compared to baseline. Signed-off-by: Srividya Desireddy <srividya.dr@samsung.com> --- mm/zswap.c | 48 +++++++++++++++++++++++++++++++++++++++++++++--- 1 file changed, 45 insertions(+), 3 deletions(-) diff --git a/mm/zswap.c b/mm/zswap.c index 067a0d6..a574008 100644 --- a/mm/zswap.c +++ b/mm/zswap.c @@ -49,6 +49,8 @@ static u64 zswap_pool_total_size; /* The number of compressed pages currently stored in zswap */ static atomic_t zswap_stored_pages = ATOMIC_INIT(0); +/* The number of zero filled pages swapped out to zswap */ +static atomic_t zswap_zero_pages = ATOMIC_INIT(0); /* * The statistics below are not protected from concurrent access for @@ -140,6 +142,8 @@ struct zswap_pool { * decompression * pool - the zswap_pool the entry's data is in * handle - zpool allocation handle that stores the compressed page data + * zeroflag - the flag is set if the content of the page is filled with + * zeros */ struct zswap_entry { struct rb_node rbnode; @@ -148,6 +152,7 @@ struct zswap_entry { unsigned int length; struct zswap_pool *pool; unsigned long handle; + unsigned char zeroflag; }; struct zswap_header { @@ -236,6 +241,7 @@ static struct zswap_entry *zswap_entry_cache_alloc(gfp_t gfp) if (!entry) return NULL; entry->refcount = 1; + entry->zeroflag = 0; RB_CLEAR_NODE(&entry->rbnode); return entry; } @@ -306,8 +312,12 @@ static void zswap_rb_erase(struct rb_root *root, struct zswap_entry *entry) */ static void zswap_free_entry(struct zswap_entry *entry) { - zpool_free(entry->pool->zpool, entry->handle); - zswap_pool_put(entry->pool); + if (entry->zeroflag) + atomic_dec(&zswap_zero_pages); + else { + zpool_free(entry->pool->zpool, entry->handle); + zswap_pool_put(entry->pool); + } zswap_entry_cache_free(entry); atomic_dec(&zswap_stored_pages); zswap_update_total_size(); @@ -877,6 +887,19 @@ static int zswap_shrink(void) return ret; } +static int zswap_is_page_zero_filled(void *ptr) +{ + unsigned int pos; + unsigned long *page; + + page = (unsigned long *)ptr; + for (pos = 0; pos != PAGE_SIZE / sizeof(*page); pos++) { + if (page[pos]) + return 0; + } + return 1; +} + /********************************* * frontswap hooks **********************************/ @@ -917,6 +940,15 @@ static int zswap_frontswap_store(unsigned type, pgoff_t offset, goto reject; } + src = kmap_atomic(page); + if (zswap_is_page_zero_filled(src)) { + kunmap_atomic(src); + entry->offset = offset; + entry->zeroflag = 1; + atomic_inc(&zswap_zero_pages); + goto insert_entry; + } + /* if entry is successfully added, it keeps the reference */ entry->pool = zswap_pool_current_get(); if (!entry->pool) { @@ -927,7 +959,6 @@ static int zswap_frontswap_store(unsigned type, pgoff_t offset, /* compress */ dst = get_cpu_var(zswap_dstmem); tfm = *get_cpu_ptr(entry->pool->tfm); - src = kmap_atomic(page); ret = crypto_comp_compress(tfm, src, PAGE_SIZE, dst, &dlen); kunmap_atomic(src); put_cpu_ptr(entry->pool->tfm); @@ -961,6 +992,7 @@ static int zswap_frontswap_store(unsigned type, pgoff_t offset, entry->handle = handle; entry->length = dlen; +insert_entry: /* map */ spin_lock(&tree->lock); do { @@ -1013,6 +1045,13 @@ static int zswap_frontswap_load(unsigned type, pgoff_t offset, } spin_unlock(&tree->lock); + if (entry->zeroflag) { + dst = kmap_atomic(page); + memset(dst, 0, PAGE_SIZE); + kunmap_atomic(dst); + goto freeentry; + } + /* decompress */ dlen = PAGE_SIZE; src = (u8 *)zpool_map_handle(entry->pool->zpool, entry->handle, @@ -1025,6 +1064,7 @@ static int zswap_frontswap_load(unsigned type, pgoff_t offset, zpool_unmap_handle(entry->pool->zpool, entry->handle); BUG_ON(ret); +freeentry: spin_lock(&tree->lock); zswap_entry_put(tree, entry); spin_unlock(&tree->lock); @@ -1133,6 +1173,8 @@ static int __init zswap_debugfs_init(void) zswap_debugfs_root, &zswap_pool_total_size); debugfs_create_atomic_t("stored_pages", S_IRUGO, zswap_debugfs_root, &zswap_stored_pages); + debugfs_create_atomic_t("zero_pages", 0444, + zswap_debugfs_root, &zswap_zero_pages); return 0; } -- 1.7.9.5 ^ permalink raw reply related [flat|nested] 5+ messages in thread
* Re: [PATCH] zswap: Zero-filled pages handling 2017-02-25 14:42 ` [PATCH] zswap: Zero-filled pages handling Srividya Desireddy @ 2017-02-25 17:18 ` Sarbojit Ganguly 2017-03-03 21:25 ` Dan Streetman [not found] ` <CGME20170225144222epcms5p15930f37372ec628420474e4d43ccfa16@epcms5p2> 0 siblings, 2 replies; 5+ messages in thread From: Sarbojit Ganguly @ 2017-02-25 17:18 UTC (permalink / raw) To: srividya.dr Cc: sjenning, ddstreet, penberg, linux-mm, linux-kernel, Dinakar Reddy Pathireddy, SHARAN ALLUR, SUNEEL KUMAR SURIMANI, JUHUN KIM, srividya.desireddy, Sarbojit Ganguly On 25 February 2017 at 20:12, Srividya Desireddy <srividya.dr@samsung.com> wrote: > From: Srividya Desireddy <srividya.dr@samsung.com> > Date: Thu, 23 Feb 2017 15:04:06 +0530 > Subject: [PATCH] zswap: Zero-filled pages handling > > Zswap is a cache which compresses the pages that are being swapped out > and stores them into a dynamically allocated RAM-based memory pool. > Experiments have shown that around 10-20% of pages stored in zswap > are zero-filled pages (i.e. contents of the page are all zeros), but > these pages are handled as normal pages by compressing and allocating > memory in the pool. > > This patch adds a check in zswap_frontswap_store() to identify zero-filled > page before compression of the page. If the page is a zero-filled page, set > zswap_entry.zeroflag and skip the compression of the page and alloction > of memory in zpool. In zswap_frontswap_load(), check if the zeroflag is > set for the page in zswap_entry. If the flag is set, memset the page with > zero. This saves the decompression time during load. > > The overall overhead caused to check for a zero-filled page is very minimal > when compared to the time saved by avoiding compression and allocation in > case of zero-filled pages. Although, compressed size of a zero-filled page > is very less, with this patch load time of a zero-filled page is reduced by > 80% when compared to baseline. Is it possible to share the benchmark details? > > Signed-off-by: Srividya Desireddy <srividya.dr@samsung.com> > --- > mm/zswap.c | 48 +++++++++++++++++++++++++++++++++++++++++++++--- > 1 file changed, 45 insertions(+), 3 deletions(-) > > diff --git a/mm/zswap.c b/mm/zswap.c > index 067a0d6..a574008 100644 > --- a/mm/zswap.c > +++ b/mm/zswap.c > @@ -49,6 +49,8 @@ > static u64 zswap_pool_total_size; > /* The number of compressed pages currently stored in zswap */ > static atomic_t zswap_stored_pages = ATOMIC_INIT(0); > +/* The number of zero filled pages swapped out to zswap */ > +static atomic_t zswap_zero_pages = ATOMIC_INIT(0); > > /* > * The statistics below are not protected from concurrent access for > @@ -140,6 +142,8 @@ struct zswap_pool { > * decompression > * pool - the zswap_pool the entry's data is in > * handle - zpool allocation handle that stores the compressed page data > + * zeroflag - the flag is set if the content of the page is filled with > + * zeros > */ > struct zswap_entry { > struct rb_node rbnode; > @@ -148,6 +152,7 @@ struct zswap_entry { > unsigned int length; > struct zswap_pool *pool; > unsigned long handle; > + unsigned char zeroflag; > }; > > struct zswap_header { > @@ -236,6 +241,7 @@ static struct zswap_entry *zswap_entry_cache_alloc(gfp_t gfp) > if (!entry) > return NULL; > entry->refcount = 1; > + entry->zeroflag = 0; > RB_CLEAR_NODE(&entry->rbnode); > return entry; > } > @@ -306,8 +312,12 @@ static void zswap_rb_erase(struct rb_root *root, struct zswap_entry *entry) > */ > static void zswap_free_entry(struct zswap_entry *entry) > { > - zpool_free(entry->pool->zpool, entry->handle); > - zswap_pool_put(entry->pool); > + if (entry->zeroflag) > + atomic_dec(&zswap_zero_pages); > + else { > + zpool_free(entry->pool->zpool, entry->handle); > + zswap_pool_put(entry->pool); > + } > zswap_entry_cache_free(entry); > atomic_dec(&zswap_stored_pages); > zswap_update_total_size(); > @@ -877,6 +887,19 @@ static int zswap_shrink(void) > return ret; > } > > +static int zswap_is_page_zero_filled(void *ptr) > +{ > + unsigned int pos; > + unsigned long *page; > + > + page = (unsigned long *)ptr; > + for (pos = 0; pos != PAGE_SIZE / sizeof(*page); pos++) { > + if (page[pos]) > + return 0; > + } > + return 1; > +} > + > /********************************* > * frontswap hooks > **********************************/ > @@ -917,6 +940,15 @@ static int zswap_frontswap_store(unsigned type, pgoff_t offset, > goto reject; > } > > + src = kmap_atomic(page); > + if (zswap_is_page_zero_filled(src)) { > + kunmap_atomic(src); > + entry->offset = offset; > + entry->zeroflag = 1; > + atomic_inc(&zswap_zero_pages); > + goto insert_entry; > + } > + > /* if entry is successfully added, it keeps the reference */ > entry->pool = zswap_pool_current_get(); > if (!entry->pool) { > @@ -927,7 +959,6 @@ static int zswap_frontswap_store(unsigned type, pgoff_t offset, > /* compress */ > dst = get_cpu_var(zswap_dstmem); > tfm = *get_cpu_ptr(entry->pool->tfm); > - src = kmap_atomic(page); > ret = crypto_comp_compress(tfm, src, PAGE_SIZE, dst, &dlen); > kunmap_atomic(src); > put_cpu_ptr(entry->pool->tfm); > @@ -961,6 +992,7 @@ static int zswap_frontswap_store(unsigned type, pgoff_t offset, > entry->handle = handle; > entry->length = dlen; > > +insert_entry: > /* map */ > spin_lock(&tree->lock); > do { > @@ -1013,6 +1045,13 @@ static int zswap_frontswap_load(unsigned type, pgoff_t offset, > } > spin_unlock(&tree->lock); > > + if (entry->zeroflag) { > + dst = kmap_atomic(page); > + memset(dst, 0, PAGE_SIZE); > + kunmap_atomic(dst); > + goto freeentry; > + } > + > /* decompress */ > dlen = PAGE_SIZE; > src = (u8 *)zpool_map_handle(entry->pool->zpool, entry->handle, > @@ -1025,6 +1064,7 @@ static int zswap_frontswap_load(unsigned type, pgoff_t offset, > zpool_unmap_handle(entry->pool->zpool, entry->handle); > BUG_ON(ret); > > +freeentry: > spin_lock(&tree->lock); > zswap_entry_put(tree, entry); > spin_unlock(&tree->lock); > @@ -1133,6 +1173,8 @@ static int __init zswap_debugfs_init(void) > zswap_debugfs_root, &zswap_pool_total_size); > debugfs_create_atomic_t("stored_pages", S_IRUGO, > zswap_debugfs_root, &zswap_stored_pages); > + debugfs_create_atomic_t("zero_pages", 0444, > + zswap_debugfs_root, &zswap_zero_pages); > > return 0; > } > -- > 1.7.9.5 -- Regards, Sarbojit -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a> ^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] zswap: Zero-filled pages handling 2017-02-25 17:18 ` Sarbojit Ganguly @ 2017-03-03 21:25 ` Dan Streetman [not found] ` <CGME20170225144222epcms5p15930f37372ec628420474e4d43ccfa16@epcms5p2> 1 sibling, 0 replies; 5+ messages in thread From: Dan Streetman @ 2017-03-03 21:25 UTC (permalink / raw) To: Sarbojit Ganguly Cc: srividya.dr, sjenning, penberg, linux-mm, linux-kernel, Dinakar Reddy Pathireddy, SHARAN ALLUR, SUNEEL KUMAR SURIMANI, JUHUN KIM, srividya.desireddy, Sarbojit Ganguly On Sat, Feb 25, 2017 at 12:18 PM, Sarbojit Ganguly <unixman.linuxboy@gmail.com> wrote: > On 25 February 2017 at 20:12, Srividya Desireddy > <srividya.dr@samsung.com> wrote: >> From: Srividya Desireddy <srividya.dr@samsung.com> >> Date: Thu, 23 Feb 2017 15:04:06 +0530 >> Subject: [PATCH] zswap: Zero-filled pages handling your email is base64-encoded; please send plain text emails. >> >> Zswap is a cache which compresses the pages that are being swapped out >> and stores them into a dynamically allocated RAM-based memory pool. >> Experiments have shown that around 10-20% of pages stored in zswap >> are zero-filled pages (i.e. contents of the page are all zeros), but 20%? that's a LOT of zero pages...which seems like applications are wasting a lot of memory. what kind of workload are you testing with? >> these pages are handled as normal pages by compressing and allocating >> memory in the pool. >> >> This patch adds a check in zswap_frontswap_store() to identify zero-filled >> page before compression of the page. If the page is a zero-filled page, set >> zswap_entry.zeroflag and skip the compression of the page and alloction >> of memory in zpool. In zswap_frontswap_load(), check if the zeroflag is >> set for the page in zswap_entry. If the flag is set, memset the page with >> zero. This saves the decompression time during load. >> >> The overall overhead caused to check for a zero-filled page is very minimal >> when compared to the time saved by avoiding compression and allocation in >> case of zero-filled pages. Although, compressed size of a zero-filled page >> is very less, with this patch load time of a zero-filled page is reduced by >> 80% when compared to baseline. > > Is it possible to share the benchmark details? Was there an answer to this? > > >> >> Signed-off-by: Srividya Desireddy <srividya.dr@samsung.com> >> --- >> mm/zswap.c | 48 +++++++++++++++++++++++++++++++++++++++++++++--- >> 1 file changed, 45 insertions(+), 3 deletions(-) >> >> diff --git a/mm/zswap.c b/mm/zswap.c >> index 067a0d6..a574008 100644 >> --- a/mm/zswap.c >> +++ b/mm/zswap.c >> @@ -49,6 +49,8 @@ >> static u64 zswap_pool_total_size; >> /* The number of compressed pages currently stored in zswap */ >> static atomic_t zswap_stored_pages = ATOMIC_INIT(0); >> +/* The number of zero filled pages swapped out to zswap */ >> +static atomic_t zswap_zero_pages = ATOMIC_INIT(0); >> >> /* >> * The statistics below are not protected from concurrent access for >> @@ -140,6 +142,8 @@ struct zswap_pool { >> * decompression >> * pool - the zswap_pool the entry's data is in >> * handle - zpool allocation handle that stores the compressed page data >> + * zeroflag - the flag is set if the content of the page is filled with >> + * zeros >> */ >> struct zswap_entry { >> struct rb_node rbnode; >> @@ -148,6 +152,7 @@ struct zswap_entry { >> unsigned int length; >> struct zswap_pool *pool; >> unsigned long handle; >> + unsigned char zeroflag; instead of a flag, we can use length == 0; the length will never be 0 for any actually compressed page. >> }; >> >> struct zswap_header { >> @@ -236,6 +241,7 @@ static struct zswap_entry *zswap_entry_cache_alloc(gfp_t gfp) >> if (!entry) >> return NULL; >> entry->refcount = 1; >> + entry->zeroflag = 0; >> RB_CLEAR_NODE(&entry->rbnode); >> return entry; >> } >> @@ -306,8 +312,12 @@ static void zswap_rb_erase(struct rb_root *root, struct zswap_entry *entry) >> */ >> static void zswap_free_entry(struct zswap_entry *entry) >> { >> - zpool_free(entry->pool->zpool, entry->handle); >> - zswap_pool_put(entry->pool); >> + if (entry->zeroflag) >> + atomic_dec(&zswap_zero_pages); >> + else { >> + zpool_free(entry->pool->zpool, entry->handle); >> + zswap_pool_put(entry->pool); >> + } >> zswap_entry_cache_free(entry); >> atomic_dec(&zswap_stored_pages); >> zswap_update_total_size(); >> @@ -877,6 +887,19 @@ static int zswap_shrink(void) >> return ret; >> } >> >> +static int zswap_is_page_zero_filled(void *ptr) >> +{ >> + unsigned int pos; >> + unsigned long *page; >> + >> + page = (unsigned long *)ptr; >> + for (pos = 0; pos != PAGE_SIZE / sizeof(*page); pos++) { >> + if (page[pos]) >> + return 0; >> + } >> + return 1; >> +} >> + >> /********************************* >> * frontswap hooks >> **********************************/ >> @@ -917,6 +940,15 @@ static int zswap_frontswap_store(unsigned type, pgoff_t offset, >> goto reject; >> } >> >> + src = kmap_atomic(page); >> + if (zswap_is_page_zero_filled(src)) { >> + kunmap_atomic(src); >> + entry->offset = offset; >> + entry->zeroflag = 1; >> + atomic_inc(&zswap_zero_pages); >> + goto insert_entry; >> + } >> + >> /* if entry is successfully added, it keeps the reference */ >> entry->pool = zswap_pool_current_get(); >> if (!entry->pool) { >> @@ -927,7 +959,6 @@ static int zswap_frontswap_store(unsigned type, pgoff_t offset, >> /* compress */ >> dst = get_cpu_var(zswap_dstmem); >> tfm = *get_cpu_ptr(entry->pool->tfm); >> - src = kmap_atomic(page); >> ret = crypto_comp_compress(tfm, src, PAGE_SIZE, dst, &dlen); >> kunmap_atomic(src); >> put_cpu_ptr(entry->pool->tfm); >> @@ -961,6 +992,7 @@ static int zswap_frontswap_store(unsigned type, pgoff_t offset, >> entry->handle = handle; >> entry->length = dlen; >> >> +insert_entry: >> /* map */ >> spin_lock(&tree->lock); >> do { >> @@ -1013,6 +1045,13 @@ static int zswap_frontswap_load(unsigned type, pgoff_t offset, >> } >> spin_unlock(&tree->lock); >> >> + if (entry->zeroflag) { >> + dst = kmap_atomic(page); >> + memset(dst, 0, PAGE_SIZE); >> + kunmap_atomic(dst); >> + goto freeentry; >> + } >> + >> /* decompress */ >> dlen = PAGE_SIZE; >> src = (u8 *)zpool_map_handle(entry->pool->zpool, entry->handle, >> @@ -1025,6 +1064,7 @@ static int zswap_frontswap_load(unsigned type, pgoff_t offset, >> zpool_unmap_handle(entry->pool->zpool, entry->handle); >> BUG_ON(ret); >> >> +freeentry: >> spin_lock(&tree->lock); >> zswap_entry_put(tree, entry); >> spin_unlock(&tree->lock); >> @@ -1133,6 +1173,8 @@ static int __init zswap_debugfs_init(void) >> zswap_debugfs_root, &zswap_pool_total_size); >> debugfs_create_atomic_t("stored_pages", S_IRUGO, >> zswap_debugfs_root, &zswap_stored_pages); >> + debugfs_create_atomic_t("zero_pages", 0444, >> + zswap_debugfs_root, &zswap_zero_pages); >> >> return 0; >> } >> -- >> 1.7.9.5 > > > > -- > Regards, > Sarbojit -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a> ^ permalink raw reply [flat|nested] 5+ messages in thread
[parent not found: <CGME20170225144222epcms5p15930f37372ec628420474e4d43ccfa16@epcms5p2>]
* [PATCH] zswap: Zero-filled pages handling [not found] ` <CGME20170225144222epcms5p15930f37372ec628420474e4d43ccfa16@epcms5p2> @ 2017-03-08 11:47 ` Srividya Desireddy 2017-03-08 14:43 ` Dan Streetman 0 siblings, 1 reply; 5+ messages in thread From: Srividya Desireddy @ 2017-03-08 11:47 UTC (permalink / raw) To: Dan Streetman, Sarbojit Ganguly Cc: sjenning, penberg, linux-mm, linux-kernel, Dinakar Reddy Pathireddy, SHARAN ALLUR, SUNEEL KUMAR SURIMANI, JUHUN KIM, Sarbojit Ganguly [-- Attachment #1: Type: text/plain, Size: 10350 bytes --] On Sat, Mar 4, 2017 at 02:55 AM, Dan Streetman <ddstreet@ieee.org> wrote: > On Sat, Feb 25, 2017 at 12:18 PM, Sarbojit Ganguly > <unixman.linuxboy@gmail.com> wrote: >> On 25 February 2017 at 20:12, Srividya Desireddy >> <srividya.dr@samsung.com> wrote: >>> From: Srividya Desireddy <srividya.dr@samsung.com> >>> Date: Thu, 23 Feb 2017 15:04:06 +0530 >>> Subject: [PATCH] zswap: Zero-filled pages handling > > your email is base64-encoded; please send plain text emails. > >>> >>> Zswap is a cache which compresses the pages that are being swapped out >>> and stores them into a dynamically allocated RAM-based memory pool. >>> Experiments have shown that around 10-20% of pages stored in zswap >>> are zero-filled pages (i.e. contents of the page are all zeros), but > > 20%? that's a LOT of zero pages...which seems like applications are > wasting a lot of memory. what kind of workload are you testing with? > I have tested this patch with different workloaded on different devices. On Ubuntu PC with 2GB RAM, while executing kernel build and other test scripts ~15% of pages in zswap were zero pages. With multimedia workload more than 20% of zswap pages were found to be zero pages. On a ARM Quad Core 32-bit device with 1.5GB RAM an average 10% of zero pages were found on launching and relaunching 15 applications. >>> these pages are handled as normal pages by compressing and allocating >>> memory in the pool. >>> >>> This patch adds a check in zswap_frontswap_store() to identify zero-filled >>> page before compression of the page. If the page is a zero-filled page, set >>> zswap_entry.zeroflag and skip the compression of the page and alloction >>> of memory in zpool. In zswap_frontswap_load(), check if the zeroflag is >>> set for the page in zswap_entry. If the flag is set, memset the page with >>> zero. This saves the decompression time during load. >>> >>> The overall overhead caused to check for a zero-filled page is very minimal >>> when compared to the time saved by avoiding compression and allocation in >>> case of zero-filled pages. Although, compressed size of a zero-filled page >>> is very less, with this patch load time of a zero-filled page is reduced by >>> 80% when compared to baseline. >> >> Is it possible to share the benchmark details? > > Was there an answer to this? > This patch is tested on a ARM Quad Core 32-bit device with 1.5GB RAM by launching and relaunching different applications. With the patch, an average of 5000 pages zero pages found in zswap out of the ~50000 pages stored in zswap and application launch time improved by ~3%. Test Parameters Baseline With patch Improvement ----------------------------------------------------------- Total RAM 1343MB 1343MB Available RAM 451MB 445MB -6MB Avg. Memfree 69MB 70MB 1MB Avg. Swap Used 226MB 215MB -11MB Avg. App entry time 644msec 623msec 3% With patch, every page swapped to zswap is checked if it is a zero page or not and for all the zero pages compression and memory allocation operations are skipped. Overall there is an improvement of 30% in zswap store time. In case of non-zero pages there is no overhead during zswap page load. For zero pages there is a improvement of more than 60% in the zswap load time as the zero page decompression is avoided. The below table shows the execution time profiling of the patch. Zswap Store Operation Baseline With patch % Improvement -------------------------------------------------------------- * Zero page check -- 22.5ms (for non-zero pages) * Zero page check -- 24ms (for zero pages) * Compression time 55ms -- (of zero pages) * Allocation time 14ms -- (to store compressed zero pages) ------------------------------------------------------------- Total 69ms 46.5ms 32% Zswap Load Operation Baseline With patch % Improvement ------------------------------------------------------------- * Decompression time 30.4ms -- (of zero pages) * Zero page check + -- 10.04ms memset operation (of zero pages) ------------------------------------------------------------- Total 30.4ms 10.04ms 66% *The execution times may vary with test device used. >> >> >>> >>> Signed-off-by: Srividya Desireddy <srividya.dr@samsung.com> >>> --- >>> mm/zswap.c | 48 +++++++++++++++++++++++++++++++++++++++++++++--- >>> 1 file changed, 45 insertions(+), 3 deletions(-) >>> >>> diff --git a/mm/zswap.c b/mm/zswap.c >>> index 067a0d6..a574008 100644 >>> --- a/mm/zswap.c >>> +++ b/mm/zswap.c >>> @@ -49,6 +49,8 @@ >>> static u64 zswap_pool_total_size; >>> /* The number of compressed pages currently stored in zswap */ >>> static atomic_t zswap_stored_pages = ATOMIC_INIT(0); >>> +/* The number of zero filled pages swapped out to zswap */ >>> +static atomic_t zswap_zero_pages = ATOMIC_INIT(0); >>> >>> /* >>> * The statistics below are not protected from concurrent access for >>> @@ -140,6 +142,8 @@ struct zswap_pool { >>> * decompression >>> * pool - the zswap_pool the entry's data is in >>> * handle - zpool allocation handle that stores the compressed page data >>> + * zeroflag - the flag is set if the content of the page is filled with >>> + * zeros >>> */ >>> struct zswap_entry { >>> struct rb_node rbnode; >>> @@ -148,6 +152,7 @@ struct zswap_entry { >>> unsigned int length; >>> struct zswap_pool *pool; >>> unsigned long handle; >>> + unsigned char zeroflag; > > instead of a flag, we can use length == 0; the length will never be 0 > for any actually compressed page. > I tested the patch using entry->length itself as flag for marking zero pages. It works fine and the functionality is same. Should I resend with this change updated? >>> }; >>> >>> struct zswap_header { >>> @@ -236,6 +241,7 @@ static struct zswap_entry *zswap_entry_cache_alloc(gfp_t gfp) >>> if (!entry) >>> return NULL; >>> entry->refcount = 1; >>> + entry->zeroflag = 0; >>> RB_CLEAR_NODE(&entry->rbnode); >>> return entry; >>> } >>> @@ -306,8 +312,12 @@ static void zswap_rb_erase(struct rb_root *root, struct zswap_entry *entry) >>> */ >>> static void zswap_free_entry(struct zswap_entry *entry) >>> { >>> - zpool_free(entry->pool->zpool, entry->handle); >>> - zswap_pool_put(entry->pool); >>> + if (entry->zeroflag) >>> + atomic_dec(&zswap_zero_pages); >>> + else { >>> + zpool_free(entry->pool->zpool, entry->handle); >>> + zswap_pool_put(entry->pool); >>> + } >>> zswap_entry_cache_free(entry); >>> atomic_dec(&zswap_stored_pages); >>> zswap_update_total_size(); >>> @@ -877,6 +887,19 @@ static int zswap_shrink(void) >>> return ret; >>> } >>> >>> +static int zswap_is_page_zero_filled(void *ptr) >>> +{ >>> + unsigned int pos; >>> + unsigned long *page; >>> + >>> + page = (unsigned long *)ptr; >>> + for (pos = 0; pos != PAGE_SIZE / sizeof(*page); pos++) { >>> + if (page[pos]) >>> + return 0; >>> + } >>> + return 1; >>> +} >>> + >>> /********************************* >>> * frontswap hooks >>> **********************************/ >>> @@ -917,6 +940,15 @@ static int zswap_frontswap_store(unsigned type, pgoff_t offset, >>> goto reject; >>> } >>> >>> + src = kmap_atomic(page); >>> + if (zswap_is_page_zero_filled(src)) { >>> + kunmap_atomic(src); >>> + entry->offset = offset; >>> + entry->zeroflag = 1; >>> + atomic_inc(&zswap_zero_pages); >>> + goto insert_entry; >>> + } >>> + >>> /* if entry is successfully added, it keeps the reference */ >>> entry->pool = zswap_pool_current_get(); >>> if (!entry->pool) { >>> @@ -927,7 +959,6 @@ static int zswap_frontswap_store(unsigned type, pgoff_t offset, >>> /* compress */ >>> dst = get_cpu_var(zswap_dstmem); >>> tfm = *get_cpu_ptr(entry->pool->tfm); >>> - src = kmap_atomic(page); >>> ret = crypto_comp_compress(tfm, src, PAGE_SIZE, dst, &dlen); >>> kunmap_atomic(src); >>> put_cpu_ptr(entry->pool->tfm); >>> @@ -961,6 +992,7 @@ static int zswap_frontswap_store(unsigned type, pgoff_t offset, >>> entry->handle = handle; >>> entry->length = dlen; >>> >>> +insert_entry: >>> /* map */ >>> spin_lock(&tree->lock); >>> do { >>> @@ -1013,6 +1045,13 @@ static int zswap_frontswap_load(unsigned type, pgoff_t offset, >>> } >>> spin_unlock(&tree->lock); >>> >>> + if (entry->zeroflag) { >>> + dst = kmap_atomic(page); >>> + memset(dst, 0, PAGE_SIZE); >>> + kunmap_atomic(dst); >>> + goto freeentry; >>> + } >>> + >>> /* decompress */ >>> dlen = PAGE_SIZE; >>> src = (u8 *)zpool_map_handle(entry->pool->zpool, entry->handle, >>> @@ -1025,6 +1064,7 @@ static int zswap_frontswap_load(unsigned type, pgoff_t offset, >>> zpool_unmap_handle(entry->pool->zpool, entry->handle); >>> BUG_ON(ret); >>> >>> +freeentry: >>> spin_lock(&tree->lock); >>> zswap_entry_put(tree, entry); >>> spin_unlock(&tree->lock); >>> @@ -1133,6 +1173,8 @@ static int __init zswap_debugfs_init(void) >>> zswap_debugfs_root, &zswap_pool_total_size); >>> debugfs_create_atomic_t("stored_pages", S_IRUGO, >>> zswap_debugfs_root, &zswap_stored_pages); >>> + debugfs_create_atomic_t("zero_pages", 0444, >>> + zswap_debugfs_root, &zswap_zero_pages); >>> >>> return 0; >>> } >>> -- >>> 1.7.9.5 >> >> >> >> -- >> Regards, >> Sarbojit ^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] zswap: Zero-filled pages handling 2017-03-08 11:47 ` Srividya Desireddy @ 2017-03-08 14:43 ` Dan Streetman 0 siblings, 0 replies; 5+ messages in thread From: Dan Streetman @ 2017-03-08 14:43 UTC (permalink / raw) To: srividya.dr Cc: Sarbojit Ganguly, sjenning, penberg, linux-mm, linux-kernel, Dinakar Reddy Pathireddy, SHARAN ALLUR, SUNEEL KUMAR SURIMANI, JUHUN KIM, Sarbojit Ganguly On Wed, Mar 8, 2017 at 6:47 AM, Srividya Desireddy <srividya.dr@samsung.com> wrote: > > On Sat, Mar 4, 2017 at 02:55 AM, Dan Streetman <ddstreet@ieee.org> wrote: >> On Sat, Feb 25, 2017 at 12:18 PM, Sarbojit Ganguly >> <unixman.linuxboy@gmail.com> wrote: >>> On 25 February 2017 at 20:12, Srividya Desireddy >>> <srividya.dr@samsung.com> wrote: >>>> From: Srividya Desireddy <srividya.dr@samsung.com> >>>> Date: Thu, 23 Feb 2017 15:04:06 +0530 >>>> Subject: [PATCH] zswap: Zero-filled pages handling >> >> your email is base64-encoded; please send plain text emails. >> >>>> >>>> Zswap is a cache which compresses the pages that are being swapped out >>>> and stores them into a dynamically allocated RAM-based memory pool. >>>> Experiments have shown that around 10-20% of pages stored in zswap >>>> are zero-filled pages (i.e. contents of the page are all zeros), but >> >> 20%? that's a LOT of zero pages...which seems like applications are >> wasting a lot of memory. what kind of workload are you testing with? >> > > I have tested this patch with different workloaded on different devices. > On Ubuntu PC with 2GB RAM, while executing kernel build and other test > scripts ~15% of pages in zswap were zero pages. With multimedia workload > more than 20% of zswap pages were found to be zero pages. > On a ARM Quad Core 32-bit device with 1.5GB RAM an average 10% of zero > pages were found on launching and relaunching 15 applications. > >>>> these pages are handled as normal pages by compressing and allocating >>>> memory in the pool. >>>> >>>> This patch adds a check in zswap_frontswap_store() to identify zero-filled >>>> page before compression of the page. If the page is a zero-filled page, set >>>> zswap_entry.zeroflag and skip the compression of the page and alloction >>>> of memory in zpool. In zswap_frontswap_load(), check if the zeroflag is >>>> set for the page in zswap_entry. If the flag is set, memset the page with >>>> zero. This saves the decompression time during load. >>>> >>>> The overall overhead caused to check for a zero-filled page is very minimal >>>> when compared to the time saved by avoiding compression and allocation in >>>> case of zero-filled pages. Although, compressed size of a zero-filled page >>>> is very less, with this patch load time of a zero-filled page is reduced by >>>> 80% when compared to baseline. >>> >>> Is it possible to share the benchmark details? >> >> Was there an answer to this? >> > > This patch is tested on a ARM Quad Core 32-bit device with 1.5GB RAM by > launching and relaunching different applications. With the patch, an > average of 5000 pages zero pages found in zswap out of the ~50000 pages > stored in zswap and application launch time improved by ~3%. > > Test Parameters Baseline With patch Improvement > ----------------------------------------------------------- > Total RAM 1343MB 1343MB > Available RAM 451MB 445MB -6MB > Avg. Memfree 69MB 70MB 1MB > Avg. Swap Used 226MB 215MB -11MB > Avg. App entry time 644msec 623msec 3% > > With patch, every page swapped to zswap is checked if it is a zero > page or not and for all the zero pages compression and memory allocation > operations are skipped. Overall there is an improvement of 30% in zswap > store time. > In case of non-zero pages there is no overhead during zswap page load. For > zero pages there is a improvement of more than 60% in the zswap load time > as the zero page decompression is avoided. > > The below table shows the execution time profiling of the patch. > > Zswap Store Operation Baseline With patch % Improvement > -------------------------------------------------------------- > * Zero page check -- 22.5ms > (for non-zero pages) > * Zero page check -- 24ms > (for zero pages) > * Compression time 55ms -- > (of zero pages) > * Allocation time 14ms -- > (to store compressed > zero pages) > ------------------------------------------------------------- > Total 69ms 46.5ms 32% > > Zswap Load Operation Baseline With patch % Improvement > ------------------------------------------------------------- > * Decompression time 30.4ms -- > (of zero pages) > * Zero page check + -- 10.04ms > memset operation > (of zero pages) > ------------------------------------------------------------- > Total 30.4ms 10.04ms 66% > > *The execution times may vary with test device used. > >>> >>> >>>> >>>> Signed-off-by: Srividya Desireddy <srividya.dr@samsung.com> >>>> --- >>>> mm/zswap.c | 48 +++++++++++++++++++++++++++++++++++++++++++++--- >>>> 1 file changed, 45 insertions(+), 3 deletions(-) >>>> >>>> diff --git a/mm/zswap.c b/mm/zswap.c >>>> index 067a0d6..a574008 100644 >>>> --- a/mm/zswap.c >>>> +++ b/mm/zswap.c >>>> @@ -49,6 +49,8 @@ >>>> static u64 zswap_pool_total_size; >>>> /* The number of compressed pages currently stored in zswap */ >>>> static atomic_t zswap_stored_pages = ATOMIC_INIT(0); >>>> +/* The number of zero filled pages swapped out to zswap */ >>>> +static atomic_t zswap_zero_pages = ATOMIC_INIT(0); >>>> >>>> /* >>>> * The statistics below are not protected from concurrent access for >>>> @@ -140,6 +142,8 @@ struct zswap_pool { >>>> * decompression >>>> * pool - the zswap_pool the entry's data is in >>>> * handle - zpool allocation handle that stores the compressed page data >>>> + * zeroflag - the flag is set if the content of the page is filled with >>>> + * zeros >>>> */ >>>> struct zswap_entry { >>>> struct rb_node rbnode; >>>> @@ -148,6 +152,7 @@ struct zswap_entry { >>>> unsigned int length; >>>> struct zswap_pool *pool; >>>> unsigned long handle; >>>> + unsigned char zeroflag; >> >> instead of a flag, we can use length == 0; the length will never be 0 >> for any actually compressed page. >> > > I tested the patch using entry->length itself as flag for marking zero pages. > It works fine and the functionality is same. Should I resend with this change > updated? yes, the patch looks good otherwise, please resend with the entry->length change. Feel free to include the testing/benchmark details in the commit message, it's interesting data. thanks! > >>>> }; >>>> >>>> struct zswap_header { >>>> @@ -236,6 +241,7 @@ static struct zswap_entry *zswap_entry_cache_alloc(gfp_t gfp) >>>> if (!entry) >>>> return NULL; >>>> entry->refcount = 1; >>>> + entry->zeroflag = 0; >>>> RB_CLEAR_NODE(&entry->rbnode); >>>> return entry; >>>> } >>>> @@ -306,8 +312,12 @@ static void zswap_rb_erase(struct rb_root *root, struct zswap_entry *entry) >>>> */ >>>> static void zswap_free_entry(struct zswap_entry *entry) >>>> { >>>> - zpool_free(entry->pool->zpool, entry->handle); >>>> - zswap_pool_put(entry->pool); >>>> + if (entry->zeroflag) >>>> + atomic_dec(&zswap_zero_pages); >>>> + else { >>>> + zpool_free(entry->pool->zpool, entry->handle); >>>> + zswap_pool_put(entry->pool); >>>> + } >>>> zswap_entry_cache_free(entry); >>>> atomic_dec(&zswap_stored_pages); >>>> zswap_update_total_size(); >>>> @@ -877,6 +887,19 @@ static int zswap_shrink(void) >>>> return ret; >>>> } >>>> >>>> +static int zswap_is_page_zero_filled(void *ptr) >>>> +{ >>>> + unsigned int pos; >>>> + unsigned long *page; >>>> + >>>> + page = (unsigned long *)ptr; >>>> + for (pos = 0; pos != PAGE_SIZE / sizeof(*page); pos++) { >>>> + if (page[pos]) >>>> + return 0; >>>> + } >>>> + return 1; >>>> +} >>>> + >>>> /********************************* >>>> * frontswap hooks >>>> **********************************/ >>>> @@ -917,6 +940,15 @@ static int zswap_frontswap_store(unsigned type, pgoff_t offset, >>>> goto reject; >>>> } >>>> >>>> + src = kmap_atomic(page); >>>> + if (zswap_is_page_zero_filled(src)) { >>>> + kunmap_atomic(src); >>>> + entry->offset = offset; >>>> + entry->zeroflag = 1; >>>> + atomic_inc(&zswap_zero_pages); >>>> + goto insert_entry; >>>> + } >>>> + >>>> /* if entry is successfully added, it keeps the reference */ >>>> entry->pool = zswap_pool_current_get(); >>>> if (!entry->pool) { >>>> @@ -927,7 +959,6 @@ static int zswap_frontswap_store(unsigned type, pgoff_t offset, >>>> /* compress */ >>>> dst = get_cpu_var(zswap_dstmem); >>>> tfm = *get_cpu_ptr(entry->pool->tfm); >>>> - src = kmap_atomic(page); >>>> ret = crypto_comp_compress(tfm, src, PAGE_SIZE, dst, &dlen); >>>> kunmap_atomic(src); >>>> put_cpu_ptr(entry->pool->tfm); >>>> @@ -961,6 +992,7 @@ static int zswap_frontswap_store(unsigned type, pgoff_t offset, >>>> entry->handle = handle; >>>> entry->length = dlen; >>>> >>>> +insert_entry: >>>> /* map */ >>>> spin_lock(&tree->lock); >>>> do { >>>> @@ -1013,6 +1045,13 @@ static int zswap_frontswap_load(unsigned type, pgoff_t offset, >>>> } >>>> spin_unlock(&tree->lock); >>>> >>>> + if (entry->zeroflag) { >>>> + dst = kmap_atomic(page); >>>> + memset(dst, 0, PAGE_SIZE); >>>> + kunmap_atomic(dst); >>>> + goto freeentry; >>>> + } >>>> + >>>> /* decompress */ >>>> dlen = PAGE_SIZE; >>>> src = (u8 *)zpool_map_handle(entry->pool->zpool, entry->handle, >>>> @@ -1025,6 +1064,7 @@ static int zswap_frontswap_load(unsigned type, pgoff_t offset, >>>> zpool_unmap_handle(entry->pool->zpool, entry->handle); >>>> BUG_ON(ret); >>>> >>>> +freeentry: >>>> spin_lock(&tree->lock); >>>> zswap_entry_put(tree, entry); >>>> spin_unlock(&tree->lock); >>>> @@ -1133,6 +1173,8 @@ static int __init zswap_debugfs_init(void) >>>> zswap_debugfs_root, &zswap_pool_total_size); >>>> debugfs_create_atomic_t("stored_pages", S_IRUGO, >>>> zswap_debugfs_root, &zswap_stored_pages); >>>> + debugfs_create_atomic_t("zero_pages", 0444, >>>> + zswap_debugfs_root, &zswap_zero_pages); >>>> >>>> return 0; >>>> } >>>> -- >>>> 1.7.9.5 >>> >>> >>> >>> -- >>> Regards, >>> Sarbojit -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a> ^ permalink raw reply [flat|nested] 5+ messages in thread
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2017-02-25 14:42 ` [PATCH] zswap: Zero-filled pages handling Srividya Desireddy
2017-02-25 17:18 ` Sarbojit Ganguly
2017-03-03 21:25 ` Dan Streetman
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2017-03-08 11:47 ` Srividya Desireddy
2017-03-08 14:43 ` Dan Streetman
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