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Patch series "zram: optimal post-processing target selection", v5. Problem: -------- Both recompression and writeback perform a very simple linear scan of all zram slots in search for post-processing (writeback or recompress) candidate slots. This often means that we pick the worst candidate for pp (post-processing), e.g. a 48 bytes object for writeback, which is nearly useless, because it only releases 48 bytes from zsmalloc pool, but consumes an entire 4K slot in the backing device. Similarly, recompression of an 48 bytes objects is unlikely to save more memory that recompression of a 3000 bytes object. Both recompression and writeback consume constrained resources (CPU time, batter, backing device storage space) and quite often have a (daily) limit on the number of items they post-process, so we should utilize those constrained resources in the most optimal way. Solution: --------- This patch reworks the way we select pp targets. We, quite clearly, want to sort all the candidates and always pick the largest, be it recompression or writeback. Especially for writeback, because the larger object we writeback the more memory we release. This series introduces concept of pp buckets and pp scan/selection. The scan step is a simple iteration over all zram->table entries, just like what we currently do, but we don't post-process a candidate slot immediately. Instead we assign it to a PP (post-processing) bucket. PP bucket is, basically, a list which holds pp candidate slots that belong to the same size class. PP buckets are 64 bytes apart, slots are not strictly sorted within a bucket there is a 64 bytes variance. The select step simply iterates over pp buckets from highest to lowest and picks all candidate slots a particular buckets contains. So this gives us sorted candidates (in linear time) and allows us to select most optimal (largest) candidates for post-processing first. This patch (of 7): This flag indicates that the slot was selected as a candidate slot for post-processing (pp) and was assigned to a pp bucket. It does not necessarily mean that the slot is currently under post-processing, but may mean so. The slot can loose its PP_SLOT flag, while still being in the pp-bucket, if it's accessed or slot_free-ed. Link: https://lkml.kernel.org/r/20240917021020.883356-1-senozhatsky@chromium.org Link: https://lkml.kernel.org/r/20240917021020.883356-2-senozhatsky@chromium.org Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org> Cc: Minchan Kim <minchan@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> |
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.