kernel/git/stable/linux.git/Documentation/admin-guide/blockdev/zram.rst, branch master

Documentation: zram: correct algo parameters configuration documentation

2026-08-25T01:42:57+00:00

zram has always reset all previously set parameters for the given algorithm in comp_params_store(). Make documentation more clear and explicitly state that all relevant/necessary parameters should be set in one configuration write. Link: https://lore.kernel.org/20260730075158.1339787-1-senozhatsky@chromium.org Signed-off-by: Sergey Senozhatsky Cc: Jonathan Corbet Cc: Minchan Kim Signed-off-by: Andrew Morton

Documentation: zram: remove sections numbering

2026-08-07T01:57:26+00:00

Those numbers are difficult to maintain and in fact we can refer to sections by their names (in html). Link: https://lore.kernel.org/20260728021229.181627-1-senozhatsky@chromium.org Signed-off-by: Sergey Senozhatsky Suggested-by: Sebastian Andrzej Siewior Reviewed-by: SJ Park Cc: Jonathan Corbet Cc: Minchan Kim Signed-off-by: Andrew Morton

zram: remove chained recompression

2026-04-05T20:53:24+00:00

Chained recompression has unpredictable behavior and is not useful in practice. First, systems usually configure just one alternative recompression algorithm, which has slower compression/decompression but better compression ratio. A single alternative algorithm doesn't need chaining. Second, even with multiple recompression algorithms, chained recompression is suboptimal. If a lower priority algorithm succeeds, the page is never attempted with a higher priority algorithm, leading to worse memory savings. If a lower priority algorithm fails, the page is still attempted with a higher priority algorithm, wasting resources on the failed lower priority attempt. In either case, the system would be better off targeting a specific priority directly. Chained recompression also significantly complicates the code. Remove it. Link: https://lkml.kernel.org/r/20260311084312.1766036-6-senozhatsky@chromium.org Signed-off-by: Sergey Senozhatsky Cc: Brian Geffon Cc: gao xu Cc: Jens Axboe Cc: Minchan Kim Signed-off-by: Andrew Morton

zram: update recompression documentation

2026-04-05T20:53:24+00:00

Emphasize usage of the `priority` parameter for recompression and explain why `algo` parameter can lead to unexpected behavior and thus is not recommended. Link: https://lkml.kernel.org/r/20260311084312.1766036-5-senozhatsky@chromium.org Signed-off-by: Sergey Senozhatsky Cc: Brian Geffon Cc: gao xu Cc: Jens Axboe Cc: Minchan Kim Signed-off-by: Andrew Morton

zram: rename writeback_compressed device attr

2026-03-04T17:44:23+00:00

Rename writeback_compressed attr to compressed_writeback to avoid possible confusion and have more natural naming. writeback_compressed may look like an alternative version of writeback while in fact writeback_compressed only sets a writeback property. Make this distinction more clear with a new compressed_writeback name. This updates a feature which is new in 7.0-rcX. Link: https://lkml.kernel.org/r/20260226025429.1042083-1-senozhatsky@chromium.org Fixes: 4c1d61389e8e ("zram: introduce writeback_compressed device attribute") Signed-off-by: Sergey Senozhatsky Suggested-by: Minchan Kim Acked-by: Minchan Kim Cc: Brian Geffon Cc: Richard Chang Cc: Suren Baghdasaryan Cc: "Christoph Böhmwalder" Cc: Jens Axboe Cc: Jonathan Corbet Cc: Lars Ellenberg Cc: Philipp Reisner Cc: Shuah Khan Signed-off-by: Andrew Morton

zram: document writeback_batch_size

2026-01-21T03:24:36+00:00

Add missing writeback_batch_size documentation. Link: https://lkml.kernel.org/r/20251201094754.4149975-4-senozhatsky@chromium.org Signed-off-by: Sergey Senozhatsky Cc: Brian Geffon Cc: David Stevens Cc: Minchan Kim Cc: Richard Chang Signed-off-by: Andrew Morton

zram: introduce writeback_compressed device attribute

2026-01-21T03:24:36+00:00

Introduce witeback_compressed device attribute to toggle compressed writeback (decompression on demand) feature. [senozhatsky@chromium.org: rewrote original patch, added documentation] Link: https://lkml.kernel.org/r/20251201094754.4149975-3-senozhatsky@chromium.org Signed-off-by: Richard Chang Co-developed-by: Sergey Senozhatsky Signed-off-by: Sergey Senozhatsky Cc: Brian Geffon Cc: David Stevens Cc: Minchan Kim Signed-off-by: Andrew Morton

Documentation: zram: update IDLE pages tracking documentation

2025-05-12T00:48:33+00:00

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

zram: modernize writeback interface

2025-05-12T00:48:09+00:00

The writeback interface supports a page_index=N parameter which performs writeback of the given page. Since we rarely need to writeback just one single page, the typical use case involves a number of writeback calls, each performing writeback of one page: echo page_index=100 > zram0/writeback ... echo page_index=200 > zram0/writeback echo page_index=500 > zram0/writeback ... echo page_index=700 > zram0/writeback One obvious downside of this is that it increases the number of syscalls. Less obvious, but a significantly more important downside, is that when given only one page to post-process zram cannot perform an optimal target selection. This becomes a critical limitation when writeback_limit is enabled, because under writeback_limit we want to guarantee the highest memory savings hence we first need to writeback pages that release the highest amount of zsmalloc pool memory. This patch adds page_indexes=LOW-HIGH parameter to the writeback interface: echo page_indexes=100-200 page_indexes=500-700 > zram0/writeback This gives zram a chance to apply an optimal target selection strategy on each iteration of the writeback loop. We also now permit multiple page_index parameters per call (previously zram would recognize only one page_index) and a mix or single pages and page ranges: echo page_index=42 page_index=99 page_indexes=100-200 \ page_indexes=500-700 > zram0/writeback Apart from that the patch also unifies parameters passing and resembles other "modern" zram device attributes (e.g. recompression), while the old interface used a mixed scheme: values-less parameters for mode and a key=value format for page_index. We still support the "old" value-less format for compatibility reasons. [senozhatsky@chromium.org: simplify parse_page_index() range checks, per Brian] nk: https://lkml.kernel.org/r/20250404015327.2427684-1-senozhatsky@chromium.org [sozhatsky@chromium.org: fix uninitialized variable in zram_writeback_slots(), per Dan] nk: https://lkml.kernel.org/r/20250409112611.1154282-1-senozhatsky@chromium.org Link: https://lkml.kernel.org/r/20250327015818.4148660-1-senozhatsky@chromium.org Signed-off-by: Sergey Senozhatsky Reviewed-by: Brian Geffon Cc: Minchan Kim Cc: Richard Chang Cc: Sergey Senozhatsky Cc: Dan Carpenter Signed-off-by: Andrew Morton

zram: remove max_comp_streams device attr

2025-03-17T05:06:33+00:00

max_comp_streams device attribute has been defunct since May 2016 when zram switched to per-CPU compression streams, remove it. Link: https://lkml.kernel.org/r/20250303022425.285971-5-senozhatsky@chromium.org Signed-off-by: Sergey Senozhatsky Cc: Hillf Danton Cc: Kairui Song Cc: Minchan Kim Cc: Sebastian Andrzej Siewior Cc: Yosry Ahmed Signed-off-by: Andrew Morton