Re: [PATCH] zram: Add a huge_idle writeback mode
From: Minchan Kim <minchan@kernel.org>
Date: 2022-03-18 16:41:52
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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?
quoted hunk ↗ jump to hunk
Signed-off-by: Brian Geffon <redacted> --- 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