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Date: Thu, 10 Mar 2022 14:29:48 +0200 From: Mike Rapoport <rppt@...nel.org> To: Yu Zhao <yuzhao@...gle.com> Cc: Andrew Morton <akpm@...ux-foundation.org>, Linus Torvalds <torvalds@...ux-foundation.org>, Andi Kleen <ak@...ux.intel.com>, Aneesh Kumar <aneesh.kumar@...ux.ibm.com>, Catalin Marinas <catalin.marinas@....com>, Dave Hansen <dave.hansen@...ux.intel.com>, Hillf Danton <hdanton@...a.com>, Jens Axboe <axboe@...nel.dk>, Jesse Barnes <jsbarnes@...gle.com>, Johannes Weiner <hannes@...xchg.org>, Jonathan Corbet <corbet@....net>, Matthew Wilcox <willy@...radead.org>, Mel Gorman <mgorman@...e.de>, Michael Larabel <Michael@...haellarabel.com>, Michal Hocko <mhocko@...nel.org>, Rik van Riel <riel@...riel.com>, Vlastimil Babka <vbabka@...e.cz>, Will Deacon <will@...nel.org>, Ying Huang <ying.huang@...el.com>, linux-arm-kernel@...ts.infradead.org, linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org, linux-mm@...ck.org, page-reclaim@...gle.com, x86@...nel.org, Brian Geffon <bgeffon@...gle.com>, Jan Alexander Steffens <heftig@...hlinux.org>, Oleksandr Natalenko <oleksandr@...alenko.name>, Steven Barrett <steven@...uorix.net>, Suleiman Souhlal <suleiman@...gle.com>, Daniel Byrne <djbyrne@....edu>, Donald Carr <d@...os-reins.com>, Holger Hoffstätte <holger@...lied-asynchrony.com>, Konstantin Kharlamov <Hi-Angel@...dex.ru>, Shuang Zhai <szhai2@...rochester.edu>, Sofia Trinh <sofia.trinh@....works>, Vaibhav Jain <vaibhav@...ux.ibm.com> Subject: Re: [PATCH v9 13/14] mm: multi-gen LRU: admin guide Hi, On Tue, Mar 08, 2022 at 07:12:30PM -0700, Yu Zhao wrote: > Add an admin guide. > > Signed-off-by: Yu Zhao <yuzhao@...gle.com> > Acked-by: Brian Geffon <bgeffon@...gle.com> > Acked-by: Jan Alexander Steffens (heftig) <heftig@...hlinux.org> > Acked-by: Oleksandr Natalenko <oleksandr@...alenko.name> > Acked-by: Steven Barrett <steven@...uorix.net> > Acked-by: Suleiman Souhlal <suleiman@...gle.com> > Tested-by: Daniel Byrne <djbyrne@....edu> > Tested-by: Donald Carr <d@...os-reins.com> > Tested-by: Holger Hoffstätte <holger@...lied-asynchrony.com> > Tested-by: Konstantin Kharlamov <Hi-Angel@...dex.ru> > Tested-by: Shuang Zhai <szhai2@...rochester.edu> > Tested-by: Sofia Trinh <sofia.trinh@....works> > Tested-by: Vaibhav Jain <vaibhav@...ux.ibm.com> > --- > Documentation/admin-guide/mm/index.rst | 1 + > Documentation/admin-guide/mm/multigen_lru.rst | 146 ++++++++++++++++++ > mm/Kconfig | 3 +- > 3 files changed, 149 insertions(+), 1 deletion(-) > create mode 100644 Documentation/admin-guide/mm/multigen_lru.rst > > diff --git a/Documentation/admin-guide/mm/index.rst b/Documentation/admin-guide/mm/index.rst > index c21b5823f126..2cf5bae62036 100644 > --- a/Documentation/admin-guide/mm/index.rst > +++ b/Documentation/admin-guide/mm/index.rst > @@ -32,6 +32,7 @@ the Linux memory management. > idle_page_tracking > ksm > memory-hotplug > + multigen_lru > nommu-mmap > numa_memory_policy > numaperf > diff --git a/Documentation/admin-guide/mm/multigen_lru.rst b/Documentation/admin-guide/mm/multigen_lru.rst > new file mode 100644 > index 000000000000..4ea6a801dc56 > --- /dev/null > +++ b/Documentation/admin-guide/mm/multigen_lru.rst > @@ -0,0 +1,146 @@ > +.. SPDX-License-Identifier: GPL-2.0 > + > +============= > +Multi-Gen LRU > +============= I'm still missing an opening paragraph the explains what is Multi-gen LRU and why users would want it. Something like Multi-gen LRU is an efficient mechanism for page reclamation. More details are of course welcome :) > +Quick start > +=========== > +Build the kernel with the following configurations. > + > +* ``CONFIG_LRU_GEN=y`` > +* ``CONFIG_LRU_GEN_ENABLED=y`` > + > +All set! > + > +Runtime options > +=============== > +``/sys/kernel/mm/lru_gen/`` contains stable ABIs described in the > +following subsections. > + > +Kill switch > +----------- > +``enable`` accepts different values to enable or disabled the ^ disable > +following components. The default value of this file depends on > +``CONFIG_LRU_GEN_ENABLED``. All the components should be enabled > +unless some of them have unforeseen side effects. Writing to > +``enable`` has no effect when a component is not supported by the > +hardware, and valid values will be accepted even when the main switch > +is off. > + > +====== =============================================================== > +Values Components > +====== =============================================================== > +0x0001 The main switch for the multi-gen LRU. > +0x0002 Clearing the accessed bit in leaf page table entries in large > + batches, when MMU sets it (e.g., on x86). This behavior can > + theoretically worsen lock contention (mmap_lock). If it is > + disabled, the multi-gen LRU will suffer a minor performance > + degradation. > +0x0004 Clearing the accessed bit in non-leaf page table entries as > + well, when MMU sets it (e.g., on x86). This behavior was not > + verified on x86 varieties other than Intel and AMD. If it is > + disabled, the multi-gen LRU will suffer a negligible > + performance degradation. > +[yYnN] Apply to all the components above. > +====== =============================================================== > + > +E.g., > +:: > + > + echo y >/sys/kernel/mm/lru_gen/enabled > + cat /sys/kernel/mm/lru_gen/enabled > + 0x0007 > + echo 5 >/sys/kernel/mm/lru_gen/enabled > + cat /sys/kernel/mm/lru_gen/enabled > + 0x0005 > + > +Thrashing prevention > +-------------------- > +Personal computers are more sensitive to thrashing because it can > +cause janks (lags when rendering UI) and negatively impact user > +experience. The multi-gen LRU offers thrashing prevention to the > +majority of laptop and desktop users who do not have ``oomd``. > + > +Users can write ``N`` to ``min_ttl_ms`` to prevent the working set of > +``N`` milliseconds from getting evicted. The OOM killer is triggered > +if this working set cannot be kept in memory. In other words, this > +option works as an adjustable pressure relief valve, and when open, it > +terminates applications that are hopefully not being used. > + > +Based on the average human detectable lag (~100ms), ``N=1000`` usually > +eliminates intolerable janks due to thrashing. Larger values like > +``N=3000`` make janks less noticeable at the risk of premature OOM > +kills. What is the default value of min_ttl_ms? > + > +Experimental features > +===================== -- Sincerely yours, Mike.
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