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Commit 8762c7dd authored by Wanpeng Li's avatar Wanpeng Li Committed by Greg Kroah-Hartman
Browse files

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: default avatarDan Magenheimer <dan.magenheimer@oracle.com>
Reviewed-by: default avatarKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: default avatarWanpeng Li <liwanp@linux.vnet.ibm.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent bdcde42d

drivers/staging/zcache/zcache-main.c

+70 −13
Original line number Diff line number Diff line
@@ -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 @@ static void *zcache_pampd_eph_create(char *data, size_t size, bool raw, 
	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 @@ static void *zcache_pampd_pers_create(char *data, size_t size, bool raw, 
	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;

}
@@ -532,6 +563,7 @@ void *zcache_pampd_create(char *data, unsigned int size, bool raw, 
 */

void zcache_pampd_create_finish(void *pampd, bool 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;

}
@@ -642,15 +692,21 @@ 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)) {

		if (!zero_filled)

			page = zbud_free_and_delist((struct zbudref *)pampd,

						true, &zsize, &zpages);

		if (page)
@@ -659,6 +715,7 @@ static void zcache_pampd_free(void *pampd, struct tmem_pool *pool, 
		dec_zcache_eph_zbytes(zsize);

		/* FIXME CONFIG_RAMSTER... check acct parameter? */

	} else {

		if (!zero_filled)

			page = zbud_free_and_delist((struct zbudref *)pampd,

						false, &zsize, &zpages);

		if (page)
@@ -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);

}