On 03/15/2013 10:34 AM, Wanpeng Li wrote:
> 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.magenhei...@oracle.com>
> Signed-off-by: Wanpeng Li <liw...@linux.vnet.ibm.com>
> ---
> drivers/staging/zcache/zcache-main.c | 81
> +++++++++++++++++++++++++++++++---
> 1 files changed, 75 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/staging/zcache/zcache-main.c
> b/drivers/staging/zcache/zcache-main.c
> index d73dd4b..6c35c7d 100644
> --- a/drivers/staging/zcache/zcache-main.c
> +++ b/drivers/staging/zcache/zcache-main.c
> @@ -59,6 +59,12 @@ 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
>
> @@ -543,7 +549,23 @@ 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_is_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 +614,8 @@ 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;
> }
> @@ -601,14 +625,31 @@ 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;
> + 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_is_zero_filled(page)) {
> + kunmap_atomic(user_mem);
> + clen = 0;
> + zero_filled = true;
> + goto got_pampd;
> + }
> + kunmap_atomic(user_mem);
> +
Maybe we can add a function for this code? It seems a bit duplicated.
> curr_pers_zpages = zcache_pers_zpages;
> /* FIXME CONFIG_RAMSTER... subtract atomic remote_pers_pages here? */
> if (!raw)
> @@ -674,6 +715,8 @@ 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;
> }
> @@ -735,7 +778,8 @@ 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);
> }
>
> /*
> @@ -780,6 +824,14 @@ 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);
> @@ -801,12 +853,21 @@ static int zcache_pampd_get_data_and_free(char *data,
> size_t *sizep, bool raw,
> struct tmem_oid *oid, uint32_t index)
> {
> int ret;
> - bool eph = !is_persistent(pool);
> + 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);
> @@ -818,6 +879,7 @@ 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)
> zcache_eph_pageframes =
> @@ -837,7 +899,7 @@ 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;
> }
> @@ -851,16 +913,23 @@ 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)
> zcache_eph_pageframes =
> @@ -883,7 +952,7 @@ 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);
> }
>
>
--
Regards,
-Bob
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