On Tue, Mar 15, 2022 at 10:22:21AM -0700, Brian Geffon wrote:
> Today it's only possible to write back as a page, idle, or huge.
> A user might want to writeback pages which are huge and idle first
> as these idle pages do not require decompression and make a good
> first pass for writeback.
Hi Brian,
I am not sure how much the decompression overhead matter for idle pages
writeback since it's already *very slow* path in zram but I agree that
it would be a good first pass since the memory saving for huge writing
would be cost efficient.
Just out of curiosity. Do you have real usecase?
>
> Signed-off-by: Brian Geffon <bgeffon@xxxxxxxxxx>
> ---
> Documentation/admin-guide/blockdev/zram.rst | 6 ++++++
> drivers/block/zram/zram_drv.c | 10 ++++++----
> 2 files changed, 12 insertions(+), 4 deletions(-)
>
> diff --git a/Documentation/admin-guide/blockdev/zram.rst b/Documentation/admin-guide/blockdev/zram.rst
> index 3e11926a4df9..af1123bfaf92 100644
> --- a/Documentation/admin-guide/blockdev/zram.rst
> +++ b/Documentation/admin-guide/blockdev/zram.rst
> @@ -343,6 +343,12 @@ Admin can request writeback of those idle pages at right timing via::
>
> With the command, zram writeback idle pages from memory to the storage.
>
> +Additionally, if a user choose to writeback only huge and idle pages
> +this can be accomplished with::
> +
> + echo huge_idle > /sys/block/zramX/writeback
> +
> +
> If admin want to write a specific page in zram device to backing device,
> they could write a page index into the interface.
>
> diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
> index cb253d80d72b..f196902ae554 100644
> --- a/drivers/block/zram/zram_drv.c
> +++ b/drivers/block/zram/zram_drv.c
> @@ -643,8 +643,8 @@ static int read_from_bdev_async(struct zram *zram, struct bio_vec *bvec,
> #define PAGE_WB_SIG "page_index="
>
> #define PAGE_WRITEBACK 0
> -#define HUGE_WRITEBACK 1
> -#define IDLE_WRITEBACK 2
> +#define HUGE_WRITEBACK (1<<0)
> +#define IDLE_WRITEBACK (1<<1)
>
>
> static ssize_t writeback_store(struct device *dev,
> @@ -664,6 +664,8 @@ static ssize_t writeback_store(struct device *dev,
> mode = IDLE_WRITEBACK;
> else if (sysfs_streq(buf, "huge"))
> mode = HUGE_WRITEBACK;
> + else if (sysfs_streq(buf, "huge_idle"))
> + mode = IDLE_WRITEBACK | HUGE_WRITEBACK;
> else {
> if (strncmp(buf, PAGE_WB_SIG, sizeof(PAGE_WB_SIG) - 1))
> return -EINVAL;
> @@ -725,10 +727,10 @@ static ssize_t writeback_store(struct device *dev,
> zram_test_flag(zram, index, ZRAM_UNDER_WB))
> goto next;
>
> - if (mode == IDLE_WRITEBACK &&
> + if (mode & IDLE_WRITEBACK &&
> !zram_test_flag(zram, index, ZRAM_IDLE))
> goto next;
> - if (mode == HUGE_WRITEBACK &&
> + if (mode & HUGE_WRITEBACK &&
> !zram_test_flag(zram, index, ZRAM_HUGE))
> goto next;
> /*
> --
> 2.35.1.723.g4982287a31-goog
>
