Commit b05f8d7e authored by Sergey Senozhatsky's avatar Sergey Senozhatsky Committed by Andrew Morton
Browse files

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: default avatarSergey Senozhatsky <senozhatsky@chromium.org>
Reported-by: default avatarShin Kawamura <kawasin@google.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Minchan Kim <minchan@kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 4a34c584

Documentation/admin-guide/blockdev/zram.rst

+21 −20
Original line number Diff line number Diff line
@@ -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