From 8762c7dde745f1de0488c6a3ed6894390303f76f Mon Sep 17 00:00:00 2001 From: Wanpeng Li Date: Tue, 2 Apr 2013 10:46:14 +0800 Subject: [PATCH] staging: zcache: zero-filled pages awareness Compression of zero-filled pages can unneccessarily cause internal fragmentation, and thus waste memory. This special case can be optimized. This patch captures zero-filled pages, and marks their corresponding zcache backing page entry as zero-filled. Whenever such zero-filled page is retrieved, we fill the page frame with zero. Acked-by: Dan Magenheimer Reviewed-by: Konrad Rzeszutek Wilk Signed-off-by: Wanpeng Li Signed-off-by: Greg Kroah-Hartman --- drivers/staging/zcache/zcache-main.c | 83 +++++++++++++++++++++++----- 1 file changed, 70 insertions(+), 13 deletions(-) diff --git a/drivers/staging/zcache/zcache-main.c b/drivers/staging/zcache/zcache-main.c index 274a48e94cfe..927d5fdaa3b1 100644 --- a/drivers/staging/zcache/zcache-main.c +++ b/drivers/staging/zcache/zcache-main.c @@ -61,6 +61,12 @@ static inline void frontswap_tmem_exclusive_gets(bool b) } #endif +/* + * mark pampd to special value in order that later + * retrieve will identify zero-filled pages + */ +#define ZERO_FILLED 0x2 + /* enable (or fix code) when Seth's patches are accepted upstream */ #define zcache_writeback_enabled 0 @@ -277,17 +283,23 @@ static void zcache_obj_free(struct tmem_obj *obj, struct tmem_pool *pool) kmem_cache_free(zcache_obj_cache, obj); } -static bool page_is_zero_filled(void *ptr) +/* + * Compressing zero-filled pages will waste memory and introduce + * serious fragmentation, skip it to avoid overhead. + */ +static bool page_is_zero_filled(struct page *p) { unsigned int pos; - unsigned long *page; - - page = (unsigned long *)ptr; + char *page; + page = kmap_atomic(p); for (pos = 0; pos < PAGE_SIZE / sizeof(*page); pos++) { - if (page[pos]) + if (page[pos]) { + kunmap_atomic(page); return false; + } } + kunmap_atomic(page); return true; } @@ -356,8 +368,15 @@ static void *zcache_pampd_eph_create(char *data, size_t size, bool raw, { void *pampd = NULL, *cdata = data; unsigned clen = size; + bool zero_filled = false; struct page *page = (struct page *)(data), *newpage; + if (page_is_zero_filled(page)) { + clen = 0; + zero_filled = true; + goto got_pampd; + } + if (!raw) { zcache_compress(page, &cdata, &clen); if (clen > zbud_max_buddy_size()) { @@ -397,6 +416,8 @@ got_pampd: inc_zcache_eph_zpages(); if (ramster_enabled && raw) ramster_count_foreign_pages(true, 1); + if (zero_filled) + pampd = (void *)ZERO_FILLED; out: return pampd; } @@ -406,6 +427,7 @@ static void *zcache_pampd_pers_create(char *data, size_t size, bool raw, { void *pampd = NULL, *cdata = data; unsigned clen = size; + bool zero_filled = false; struct page *page = (struct page *)(data), *newpage; unsigned long zbud_mean_zsize; unsigned long curr_pers_zpages, total_zsize; @@ -414,6 +436,13 @@ static void *zcache_pampd_pers_create(char *data, size_t size, bool raw, BUG_ON(!ramster_enabled); goto create_pampd; } + + if (page_is_zero_filled(page)) { + clen = 0; + zero_filled = true; + goto got_pampd; + } + curr_pers_zpages = zcache_pers_zpages; /* FIXME CONFIG_RAMSTER... subtract atomic remote_pers_pages here? */ if (!raw) @@ -471,6 +500,8 @@ got_pampd: inc_zcache_pers_zbytes(clen); if (ramster_enabled && raw) ramster_count_foreign_pages(false, 1); + if (zero_filled) + pampd = (void *)ZERO_FILLED; out: return pampd; } @@ -532,7 +563,8 @@ out: */ void zcache_pampd_create_finish(void *pampd, bool eph) { - zbud_create_finish((struct zbudref *)pampd, eph); + if (pampd != (void *)ZERO_FILLED) + zbud_create_finish((struct zbudref *)pampd, eph); } /* @@ -577,6 +609,14 @@ static int zcache_pampd_get_data(char *data, size_t *sizep, bool raw, BUG_ON(preemptible()); BUG_ON(eph); /* fix later if shared pools get implemented */ BUG_ON(pampd_is_remote(pampd)); + + if (pampd == (void *)ZERO_FILLED) { + handle_zero_filled_page(data); + if (!raw) + *sizep = PAGE_SIZE; + return 0; + } + if (raw) ret = zbud_copy_from_zbud(data, (struct zbudref *)pampd, sizep, eph); @@ -597,13 +637,22 @@ static int zcache_pampd_get_data_and_free(char *data, size_t *sizep, bool raw, void *pampd, struct tmem_pool *pool, struct tmem_oid *oid, uint32_t index) { - int ret; - bool eph = !is_persistent(pool); + int ret = 0; + bool eph = !is_persistent(pool), zero_filled = false; struct page *page = NULL; unsigned int zsize, zpages; BUG_ON(preemptible()); BUG_ON(pampd_is_remote(pampd)); + + if (pampd == (void *)ZERO_FILLED) { + handle_zero_filled_page(data); + zero_filled = true; + if (!raw) + *sizep = PAGE_SIZE; + goto zero_fill; + } + if (raw) ret = zbud_copy_from_zbud(data, (struct zbudref *)pampd, sizep, eph); @@ -615,6 +664,7 @@ static int zcache_pampd_get_data_and_free(char *data, size_t *sizep, bool raw, } page = zbud_free_and_delist((struct zbudref *)pampd, eph, &zsize, &zpages); +zero_fill: if (eph) { if (page) dec_zcache_eph_pageframes(); @@ -628,7 +678,7 @@ static int zcache_pampd_get_data_and_free(char *data, size_t *sizep, bool raw, } if (!is_local_client(pool->client)) ramster_count_foreign_pages(eph, -1); - if (page) + if (page && !zero_filled) zcache_free_page(page); return ret; } @@ -642,16 +692,22 @@ static void zcache_pampd_free(void *pampd, struct tmem_pool *pool, { struct page *page = NULL; unsigned int zsize, zpages; + bool zero_filled = false; BUG_ON(preemptible()); - if (pampd_is_remote(pampd)) { + + if (pampd == (void *)ZERO_FILLED) + zero_filled = true; + + if (pampd_is_remote(pampd) && !zero_filled) { BUG_ON(!ramster_enabled); pampd = ramster_pampd_free(pampd, pool, oid, index, acct); if (pampd == NULL) return; } if (is_ephemeral(pool)) { - page = zbud_free_and_delist((struct zbudref *)pampd, + if (!zero_filled) + page = zbud_free_and_delist((struct zbudref *)pampd, true, &zsize, &zpages); if (page) dec_zcache_eph_pageframes(); @@ -659,7 +715,8 @@ static void zcache_pampd_free(void *pampd, struct tmem_pool *pool, dec_zcache_eph_zbytes(zsize); /* FIXME CONFIG_RAMSTER... check acct parameter? */ } else { - page = zbud_free_and_delist((struct zbudref *)pampd, + if (!zero_filled) + page = zbud_free_and_delist((struct zbudref *)pampd, false, &zsize, &zpages); if (page) dec_zcache_pers_pageframes(); @@ -668,7 +725,7 @@ static void zcache_pampd_free(void *pampd, struct tmem_pool *pool, } if (!is_local_client(pool->client)) ramster_count_foreign_pages(is_ephemeral(pool), -1); - if (page) + if (page && !zero_filled) zcache_free_page(page); } -- 2.39.5