On Fri, Mar 29, 2024 at 5:40 AM Sergey Senozhatsky
<senozhatsky@xxxxxxxxxxxx> wrote:
>
> 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.
>
> Signed-off-by: Sergey Senozhatsky <senozhatsky@xxxxxxxxxxxx>
Acked-by: Brian Geffon <bgeffon@xxxxxxxxxx>
>
> ---
> Documentation/admin-guide/blockdev/zram.rst | 5 ++++
> drivers/block/zram/zram_drv.c | 31 +++++++++++++++++++--
> 2 files changed, 33 insertions(+), 3 deletions(-)
>
> diff --git a/Documentation/admin-guide/blockdev/zram.rst b/Documentation/admin-guide/blockdev/zram.rst
> index ee2b0030d416..091e8bb38887 100644
> --- a/Documentation/admin-guide/blockdev/zram.rst
> +++ b/Documentation/admin-guide/blockdev/zram.rst
> @@ -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,
> diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
> index f0639df6cd18..4cf38f7d3e0a 100644
> --- a/drivers/block/zram/zram_drv.c
> +++ b/drivers/block/zram/zram_drv.c
> @@ -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) {
> --
> 2.44.0.478.gd926399ef9-goog
>
