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Patch series "mm/page_alloc: pcp->batch cleanups", v2. Two small cleanups for mm/page_alloc. Patch 1 cleans up a misleading comment about how pcp->batch is calculated, and folds in the calculation to increase clarity. No functional change intended. Patch 2 corrects zones from reporting that their pcp->batch is 0 when it is actually 1. Namely, corrects ZONE_DMA from reporting that its batch size is 0. This patch (of 2): Recently while working on another patch about batching free_pcppages_bulk [1], I was curious why pcp->batch was always 63 on my machine. This led me to zone_batchsize(), where I found this set of lines to determine what the batch size should be for the host: batch = min(zone_managed_pages(zone) >> 10, SZ_1M / PAGE_SIZE); batch /= 4; /* We effectively *= 4 below */ if (batch < 1) batch = 1; All of this is good, except the comment above which says "We effectively *= 4 below". Nowhere else in the function zone_batchsize(), is there a corresponding multipliation by 4. Looking into the history of this, it seems like Dave Hansen had also noticed this back in 2013 [1]. Turns out there *used* to be a corresponding *= 4, which was turned into a *= 6 later on to be used in pageset_setup_from_batch_size(), which no longer exists. Despite this mismatch not being corrected in the comments, it seems that getting rid of the /= 4 leads to a performance regression on machines with less than 250G memory and 176 processors. As such, let us preserve the functionality but clean up the comments. Fold the /= 4 into the calculation above: bitshift by 10+2=12, and instead of dividing 1MB, divide 256KB and adjust the comments accordingly. No functional change intended. Link: https://lkml.kernel.org/r/20251009192933.3756712-1-joshua.hahnjy@gmail.com Link: https://lkml.kernel.org/r/20251009192933.3756712-2-joshua.hahnjy@gmail.com Link: https://lore.kernel.org/all/20251002204636.4016712-1-joshua.hahnjy@gmail.com/ [1] Signed-off-by: Joshua Hahn <joshua.hahnjy@gmail.com> Suggested-by: Dave Hansen <dave.hansen@intel.com> Acked-by: Vlastimil Babka <vbabka@suse.cz> Cc: Brendan Jackman <jackmanb@google.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Michal Hocko <mhocko@suse.com> Cc: Suren Baghdasaryan <surenb@google.com> Cc: Zi Yan <ziy@nvidia.com> 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.