On Sat, Mar 16, 2013 at 10:12:25PM +0800, Bob Liu wrote:
>
>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.magenheimer@xxxxxxxxxx>
>> Signed-off-by: Wanpeng Li <liwanp@xxxxxxxxxxxxxxxxxx>
>> ---
>> 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);
>> +
>
Hi Bob,
>Maybe we can add a function for this code? It seems a bit duplicated.
>
Great point! I will introduce a separate function to handle zero filled
capture stuff.
Regards,
Wanpeng Li
>> 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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