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Documentation: zram: update IDLE pages tracking documentation

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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 <senozhatsky@chromium.org>
Reported-by: Shin Kawamura <kawasin@google.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Minchan Kim <minchan@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Sergey Senozhatsky 2025-04-16 13:27:59 +09:00 committed by Andrew Morton
parent 4a34c584d8
commit b05f8d7e07
1 changed files with 21 additions and 20 deletions
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41
Documentation/admin-guide/blockdev/zram.rst
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@ -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