Commit 34efe1c3 authored by Sergey Senozhatsky's avatar Sergey Senozhatsky Committed by Andrew Morton
Browse files

zram: add max_pages param to recompression 

Introduce "max_pages" param to recompress device attribute which sets an
upper limit on the number of entries (pages) zram attempts to recompress
(in this particular recompression call).  S/W recompression can be quite
expensive so limiting the number of pages recompress touches can be quite
helpful.

Link: https://lkml.kernel.org/r/20240329094050.2815699-1-senozhatsky@chromium.org


Signed-off-by: default avatarSergey Senozhatsky <senozhatsky@chromium.org>
Acked-by: default avatarBrian Geffon <bgeffon@google.com>
Cc: Minchan Kim <minchan@kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent ba42b524

Documentation/admin-guide/blockdev/zram.rst

+5 −0
Original line number Diff line number Diff line
@@ -466,6 +466,11 @@ of equal or greater size::: 
	#recompress idle pages larger than 2000 bytes

	echo "type=idle threshold=2000" > /sys/block/zramX/recompress



It is also possible to limit the number of pages zram re-compression will

attempt to recompress:::



	echo "type=huge_idle max_pages=42" > /sys/block/zramX/recompress



Recompression of idle pages requires memory tracking.



During re-compression for every page, that matches re-compression criteria,

drivers/block/zram/zram_drv.c

+28 −3
Original line number Diff line number Diff line
@@ -1568,7 +1568,8 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, 
 * Corresponding ZRAM slot should be locked.

 */

static int zram_recompress(struct zram *zram, u32 index, struct page *page,

			   u32 threshold, u32 prio, u32 prio_max)

			   u64 *num_recomp_pages, u32 threshold, u32 prio,

			   u32 prio_max)

{

	struct zcomp_strm *zstrm = NULL;

	unsigned long handle_old;
@@ -1645,6 +1646,15 @@ static int zram_recompress(struct zram *zram, u32 index, struct page *page, 
	if (!zstrm)

		return 0;



	/*

	 * Decrement the limit (if set) on pages we can recompress, even

	 * when current recompression was unsuccessful or did not compress

	 * the page below the threshold, because we still spent resources

	 * on it.

	 */

	if (*num_recomp_pages)

		*num_recomp_pages -= 1;



	if (class_index_new >= class_index_old) {

		/*

		 * Secondary algorithms failed to re-compress the page
@@ -1710,6 +1720,7 @@ static ssize_t recompress_store(struct device *dev, 
	struct zram *zram = dev_to_zram(dev);

	unsigned long nr_pages = zram->disksize >> PAGE_SHIFT;

	char *args, *param, *val, *algo = NULL;

	u64 num_recomp_pages = ULLONG_MAX;

	u32 mode = 0, threshold = 0;

	unsigned long index;

	struct page *page;
@@ -1732,6 +1743,17 @@ static ssize_t recompress_store(struct device *dev, 
			continue;

		}



		if (!strcmp(param, "max_pages")) {

			/*

			 * Limit the number of entries (pages) we attempt to

			 * recompress.

			 */

			ret = kstrtoull(val, 10, &num_recomp_pages);

			if (ret)

				return ret;

			continue;

		}



		if (!strcmp(param, "threshold")) {

			/*

			 * We will re-compress only idle objects equal or
@@ -1788,6 +1810,9 @@ static ssize_t recompress_store(struct device *dev, 
	for (index = 0; index < nr_pages; index++) {

		int err = 0;



		if (!num_recomp_pages)

			break;



		zram_slot_lock(zram, index);



		if (!zram_allocated(zram, index))
@@ -1807,8 +1832,8 @@ static ssize_t recompress_store(struct device *dev, 
		    zram_test_flag(zram, index, ZRAM_INCOMPRESSIBLE))

			goto next;



		err = zram_recompress(zram, index, page, threshold,

				      prio, prio_max);

		err = zram_recompress(zram, index, page, &num_recomp_pages,

				      threshold, prio, prio_max);

next:

		zram_slot_unlock(zram, index);

		if (err) {