From b05f8d7e077952d14acb63e3ccdf5f64404b59a4 Mon Sep 17 00:00:00 2001 From: Sergey Senozhatsky Date: Wed, 16 Apr 2025 13:27:59 +0900 Subject: [PATCH] Documentation: zram: update IDLE pages tracking documentation Move IDLE pages tracking into a separate chapter because there are multiple features that use (or depend on) it either in built-in variant ("mark all") or in extended variant (ac-time tracking). In addition, recompression doesn't require memory tracking to be enabled in order to be able to perform idle recompression. Link: https://lkml.kernel.org/r/20250416042833.3858827-1-senozhatsky@chromium.org Signed-off-by: Sergey Senozhatsky Reported-by: Shin Kawamura Cc: Jonathan Corbet Cc: Minchan Kim Signed-off-by: Andrew Morton --- Documentation/admin-guide/blockdev/zram.rst | 41 +++++++++++---------- 1 file changed, 21 insertions(+), 20 deletions(-) diff --git a/Documentation/admin-guide/blockdev/zram.rst b/Documentation/admin-guide/blockdev/zram.rst index b8d36134a151e..3e273c1bb749d 100644 --- a/Documentation/admin-guide/blockdev/zram.rst +++ b/Documentation/admin-guide/blockdev/zram.rst @@ -317,6 +317,26 @@ a single line of text and contains the following stats separated by whitespace: Optional Feature ================ +IDLE pages tracking +------------------- + +zram has built-in support for idle pages tracking (that is, allocated but +not used pages). This feature is useful for e.g. zram writeback and +recompression. In order to mark pages as idle, execute the following command:: + + echo all > /sys/block/zramX/idle + +This will mark all allocated zram pages as idle. The idle mark will be +removed only when the page (block) is accessed (e.g. overwritten or freed). +Additionally, when CONFIG_ZRAM_TRACK_ENTRY_ACTIME is enabled, pages can be +marked as idle based on how many seconds have passed since the last access to +a particular zram page:: + + echo 86400 > /sys/block/zramX/idle + +In this example, all pages which haven't been accessed in more than 86400 +seconds (one day) will be marked idle. + writeback --------- @@ -331,24 +351,7 @@ If admin wants to use incompressible page writeback, they could do it via:: echo huge > /sys/block/zramX/writeback -To use idle page writeback, first, user need to declare zram pages -as idle:: - - echo all > /sys/block/zramX/idle - -From now on, any pages on zram are idle pages. The idle mark -will be removed until someone requests access of the block. -IOW, unless there is access request, those pages are still idle pages. -Additionally, when CONFIG_ZRAM_TRACK_ENTRY_ACTIME is enabled pages can be -marked as idle based on how long (in seconds) it's been since they were -last accessed:: - - echo 86400 > /sys/block/zramX/idle - -In this example all pages which haven't been accessed in more than 86400 -seconds (one day) will be marked idle. - -Admin can request writeback of those idle pages at right timing via:: +Admin can request writeback of idle pages at right timing via:: echo idle > /sys/block/zramX/writeback @@ -499,8 +502,6 @@ 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, ZRAM iterates the list of registered alternative compression algorithms in order of their priorities. ZRAM stops either when re-compression was -- 2.39.5