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calculate_totalreserve_pages() currently finds the maximum lowmem_reserve[j] for a zone by scanning the full forward range [j = zone_idx .. MAX_NR_ZONES). However, for a given zone i, the lowmem_reserve[j] array (for j > i) is naturally expected to form a monotonically non-decreasing sequence in j, not as an implementation detail, but as a consequence that naturally arises from the semantics of lowmem_reserve[]. For zone "i", lowmem_reserve[j] expresses how many pages in zone i must effectively be kept in reserve when deciding whether an allocation class that may allocate from zones up to j is allowed to fall back into i. It protects less flexible allocation classes (which cannot use higher zones) from being starved by more flexible ones. Viewed from this semantics, it is natural to expect a partial ordering in j: as j increases, the allocation class gains access to a strictly larger set of fallback zones. Therefore lowmem_reserve[j] is expected to be monotonically non-decreasing in j: more flexible allocation classes must not be allowed to deplete low zones more aggressively than less flexible ones. In other words, if lowmem_reserve[j] were ever observed to *decrease* as j grows, that would be unexpected from the reserve semantics' point of view and would likely indicate a semantic change or a misconfiguration. The current implementation in setup_per_zone_lowmem_reserve() reflects this policy by accumulating managed pages from higher zones and applying the configured ratio, which results in a non-decreasing sequence. This patch makes calculate_totalreserve_pages() rely on that monotonicity explicitly and finds the maximum reserve value by scanning backward and stopping at the first non-zero entry. This avoids unnecessary iteration and reflects the conceptual model more directly. No functional behavior changes. To maintain this assumption explicitly, a comment is added next to setup_per_zone_lowmem_reserve() documenting the monotonicity expectation and noting that calculate_totalreserve_pages() relies on it. Link: https://lkml.kernel.org/r/tencent_EB0FED91B01B1F8B6DAEE96719C5F5797F07@qq.com Signed-off-by: fujunjie <fujunjie1@qq.com> Acked-by: Zi Yan <ziy@nvidia.com> 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: Vlastimil Babka <vbabka@suse.cz> 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.