[PATCH 2/4] zcache: zero-filled pages awareness
From: Wanpeng Li
Date: Wed Mar 13 2013 - 03:06:33 EST
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.
Signed-off-by: Wanpeng Li <liwanp@xxxxxxxxxxxxxxxxxx>
---
drivers/staging/zcache/tmem.c | 4 +-
drivers/staging/zcache/tmem.h | 5 ++
drivers/staging/zcache/zcache-main.c | 87 ++++++++++++++++++++++++++++++----
3 files changed, 85 insertions(+), 11 deletions(-)
diff --git a/drivers/staging/zcache/tmem.c b/drivers/staging/zcache/tmem.c
index a2b7e03..62468ea 100644
--- a/drivers/staging/zcache/tmem.c
+++ b/drivers/staging/zcache/tmem.c
@@ -597,7 +597,9 @@ int tmem_put(struct tmem_pool *pool, struct tmem_oid *oidp, uint32_t index,
if (unlikely(ret == -ENOMEM))
/* may have partially built objnode tree ("stump") */
goto delete_and_free;
- (*tmem_pamops.create_finish)(pampd, is_ephemeral(pool));
+ if (pampd != (void *)ZERO_FILLED)
+ (*tmem_pamops.create_finish)(pampd, is_ephemeral(pool));
+
goto out;
delete_and_free:
diff --git a/drivers/staging/zcache/tmem.h b/drivers/staging/zcache/tmem.h
index adbe5a8..6719dbd 100644
--- a/drivers/staging/zcache/tmem.h
+++ b/drivers/staging/zcache/tmem.h
@@ -204,6 +204,11 @@ struct tmem_handle {
uint16_t client_id;
};
+/*
+ * mark pampd to special vaule in order that later
+ * retrieve will identify zero-filled pages
+ */
+#define ZERO_FILLED 0x2
/* pampd abstract datatype methods provided by the PAM implementation */
struct tmem_pamops {
diff --git a/drivers/staging/zcache/zcache-main.c b/drivers/staging/zcache/zcache-main.c
index b71e033..ed5ef26 100644
--- a/drivers/staging/zcache/zcache-main.c
+++ b/drivers/staging/zcache/zcache-main.c
@@ -543,7 +543,23 @@ 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;
+ char *user_mem;
+
+ user_mem = kmap_atomic(page);
+
+ /*
+ * Compressing zero-filled pages will waste memory and introduce
+ * serious fragmentation, skip it to avoid overhead
+ */
+ if (page_zero_filled(user_mem)) {
+ kunmap_atomic(user_mem);
+ clen = 0;
+ zero_filled = true;
+ goto got_pampd;
+ }
+ kunmap_atomic(user_mem);
if (!raw) {
zcache_compress(page, &cdata, &clen);
@@ -592,6 +608,8 @@ got_pampd:
zcache_eph_zpages_max = zcache_eph_zpages;
if (ramster_enabled && raw)
ramster_count_foreign_pages(true, 1);
+ if (zero_filled)
+ pampd = (void *)ZERO_FILLED;
out:
return pampd;
}
@@ -600,15 +618,31 @@ static void *zcache_pampd_pers_create(char *data, size_t size, bool raw,
struct tmem_handle *th)
{
void *pampd = NULL, *cdata = data;
- unsigned clen = size;
+ unsigned clen = size, zero_filled = 0;
struct page *page = (struct page *)(data), *newpage;
unsigned long zbud_mean_zsize;
unsigned long curr_pers_zpages, total_zsize;
+ char *user_mem;
if (data == NULL) {
BUG_ON(!ramster_enabled);
goto create_pampd;
}
+
+ user_mem = kmap_atomic(page);
+
+ /*
+ * Compressing zero-filled pages will waste memory and introduce
+ * serious fragmentation, skip it to avoid overhead
+ */
+ if (page_zero_filled(page)) {
+ kunmap_atomic(user_mem);
+ clen = 0;
+ zero_filled = 1;
+ goto got_pampd;
+ }
+ kunmap_atomic(user_mem);
+
curr_pers_zpages = zcache_pers_zpages;
/* FIXME CONFIG_RAMSTER... subtract atomic remote_pers_pages here? */
if (!raw)
@@ -674,6 +708,8 @@ got_pampd:
zcache_pers_zbytes_max = zcache_pers_zbytes;
if (ramster_enabled && raw)
ramster_count_foreign_pages(false, 1);
+ if (zero_filled)
+ pampd = (void *)ZERO_FILLED;
out:
return pampd;
}
@@ -780,6 +816,14 @@ 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_page(data);
+ if (!raw)
+ *sizep = PAGE_SIZE;
+ return 0;
+ }
+
if (raw)
ret = zbud_copy_from_zbud(data, (struct zbudref *)pampd,
sizep, eph);
@@ -800,13 +844,24 @@ 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_page(data);
+ zero_filled = true;
+ zsize = 0;
+ zpages = 1;
+ if (!raw)
+ *sizep = PAGE_SIZE;
+ goto zero_fill;
+ }
+
if (raw)
ret = zbud_copy_from_zbud(data, (struct zbudref *)pampd,
sizep, eph);
@@ -818,8 +873,9 @@ 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)
+ if (page || zero_filled)
zcache_eph_pageframes =
atomic_dec_return(&zcache_eph_pageframes_atomic);
zcache_eph_zpages =
@@ -827,7 +883,7 @@ static int zcache_pampd_get_data_and_free(char *data, size_t *sizep, bool raw,
zcache_eph_zbytes =
atomic_long_sub_return(zsize, &zcache_eph_zbytes_atomic);
} else {
- if (page)
+ if (page || zero_filled)
zcache_pers_pageframes =
atomic_dec_return(&zcache_pers_pageframes_atomic);
zcache_pers_zpages =
@@ -837,7 +893,7 @@ 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;
}
@@ -851,18 +907,29 @@ 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;
+ zsize = 0;
+ zpages = 1;
+ }
+
+ 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)
+ if (page || zero_filled)
zcache_eph_pageframes =
atomic_dec_return(&zcache_eph_pageframes_atomic);
zcache_eph_zpages =
@@ -883,7 +950,7 @@ 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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