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 <dan.magenheimer@xxxxxxxxxx>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Signed-off-by: Wanpeng Li <liwanp@xxxxxxxxxxxxxxxxxx>
---
drivers/staging/zcache/zcache-main.c | 80 ++++++++++++++++++++++++++++-----
1 files changed, 68 insertions(+), 12 deletions(-)
diff --git a/drivers/staging/zcache/zcache-main.c b/drivers/staging/zcache/zcache-main.c
index 86ead8d..050a99f 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;
}
@@ -355,8 +367,15 @@ 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()) {
@@ -396,6 +415,8 @@ 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;
}
@@ -405,6 +426,7 @@ 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;
@@ -413,6 +435,13 @@ 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)
@@ -470,6 +499,8 @@ 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;
}
@@ -531,7 +562,8 @@ 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);
}
/*
@@ -576,6 +608,14 @@ 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);
@@ -596,13 +636,22 @@ 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);
@@ -614,6 +663,7 @@ 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();
@@ -627,7 +677,7 @@ 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;
}
@@ -641,16 +691,22 @@ 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();
@@ -667,7 +723,7 @@ 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);
}
--
1.7.7.6
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