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Johannes Weiner 3f1509c57b Revert "mm/vmscan: never demote for memcg reclaim" This reverts commit `3a235693d3`. Its premise was that cgroup reclaim cares about freeing memory inside the cgroup, and demotion just moves them around within the cgroup limit. Hence, pages from toptier nodes should be reclaimed directly. However, with NUMA balancing now doing tier promotions, demotion is part of the page aging process. Global reclaim demotes the coldest toptier pages to secondary memory, where their life continues and from which they have a chance to get promoted back. Essentially, tiered memory systems have an LRU order that spans multiple nodes. When cgroup reclaims pages coming off the toptier directly, there can be colder pages on lower tier nodes that were demoted by global reclaim. This is an aging inversion, not unlike if cgroups were to reclaim directly from the active lists while there are inactive pages. Proactive reclaim is another factor. The goal of that it is to offload colder pages from expensive RAM to cheaper storage. When lower tier memory is available as an intermediate layer, we want offloading to take advantage of it instead of bypassing to storage. Revert the patch so that cgroups respect the LRU order spanning the memory hierarchy. Of note is a specific undercommit scenario, where all cgroup limits in the system add up to <= available toptier memory. In that case, shuffling pages out to lower tiers first to reclaim them from there is inefficient. This is something could be optimized/short-circuited later on (although care must be taken not to accidentally recreate the aging inversion). Let's ensure correctness first. Link: https://lkml.kernel.org/r/20220518190911.82400-1-hannes@cmpxchg.org Signed-off-by: Johannes Weiner <hannes@cmpxchg.org> Acked-by: Dave Hansen <dave.hansen@linux.intel.com> Reviewed-by: Yang Shi <shy828301@gmail.com> Acked-by: Roman Gushchin <roman.gushchin@linux.dev> Reviewed-by: "Huang, Ying" <ying.huang@intel.com> Reviewed-by: Muchun Song <songmuchun@bytedance.com> Acked-by: Michal Hocko <mhocko@suse.com> Acked-by: Shakeel Butt <shakeelb@google.com> Acked-by: Tim Chen <tim.c.chen@linux.intel.com> Cc: Zi Yan <ziy@nvidia.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>		2022-05-25 10:47:48 -07:00
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drivers	zram: fix Kconfig dependency warning	2022-05-25 10:47:47 -07:00
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include	include/trace/events/percpu.h: cleanup for "percpu: improve percpu_alloc_percpu event trace"	2022-05-25 10:47:48 -07:00
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mm	Revert "mm/vmscan: never demote for memcg reclaim"	2022-05-25 10:47:48 -07:00
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tools	cgroup: fix an error handling path in alloc_pagecache_max_30M()	2022-05-25 10:47:46 -07:00
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MAINTAINERS	MAINTAINERS: add Muchun as co-maintainer for HugeTLB	2022-05-25 10:47:47 -07:00
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README

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 Restructured Text 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.