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Message-ID: <76e951ec-5043-4e89-8a5f-efdeaec4bb81@linux.alibaba.com>
Date: Wed, 16 Apr 2025 16:24:15 +0800
From: Baolin Wang <baolin.wang@...ux.alibaba.com>
To: Barry Song <21cnbao@...il.com>, Zi Yan <ziy@...dia.com>,
Tangquan Zheng <zhengtangquan@...o.com>
Cc: akpm@...ux-foundation.org, linux-mm@...ck.org,
linux-kernel@...r.kernel.org, Barry Song <v-songbaohua@...o.com>,
David Hildenbrand <david@...hat.com>, Johannes Weiner <hannes@...xchg.org>,
Matthew Wilcox <willy@...radead.org>, Oscar Salvador <osalvador@...e.de>,
Ryan Roberts <ryan.roberts@....com>
Subject: Re: [RFC PATCH] mm: don't promote exclusive file folios of dying
processes
On 2025/4/16 15:48, Barry Song wrote:
> On Sun, Apr 13, 2025 at 12:31 AM Zi Yan <ziy@...dia.com> wrote:
>>
>> On 12 Apr 2025, at 4:58, Barry Song wrote:
>>
>>> From: Barry Song <v-songbaohua@...o.com>
>>>
>>> Promoting exclusive file folios of a dying process is unnecessary and
>>> harmful. For example, while Firefox is killed and LibreOffice is
>>> launched, activating Firefox's young file-backed folios makes it
>>> harder to reclaim memory that LibreOffice doesn't use at all.
>>>
>>> An exiting process is unlikely to be restarted right away—it's
>>> either terminated by the user or killed by the OOM handler.
>>
>> The proposal looks reasonable to me. Do you have any performance number
>> about the improvement?
>
> Tangquan ran the test on Android phones and saw 3% improvement on
> refault/thrashing things:
Good.
> w/o patch w/patch
> workingset_refault_anon 2215933 2146602 3.13%
> workingset_refault_file 9859208 9646518 2.16%
> pswpin 2411086 2337790 3.04%
> pswpout 6482838 6264865 3.36%
>
> A further demotion of exclusive file folios can improvement more, but
> might be controversial. it could be a separate patch later.
>
>>
>>>
>>> Cc: Baolin Wang <baolin.wang@...ux.alibaba.com>
>>> Cc: David Hildenbrand <david@...hat.com>
>>> Cc: Johannes Weiner <hannes@...xchg.org>
>>> Cc: Matthew Wilcox (Oracle) <willy@...radead.org>
>>> Cc: Oscar Salvador <osalvador@...e.de>
>>> Cc: Ryan Roberts <ryan.roberts@....com>
>>> Cc: Zi Yan <ziy@...dia.com>
>>> Signed-off-by: Barry Song <v-songbaohua@...o.com>
>>> ---
>>> mm/huge_memory.c | 4 ++--
>>> mm/internal.h | 19 +++++++++++++++++++
>>> mm/memory.c | 9 ++++++++-
>>> 3 files changed, 29 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
>>> index e97a97586478..05b83d2fcbb6 100644
>>> --- a/mm/huge_memory.c
>>> +++ b/mm/huge_memory.c
>>> @@ -2264,8 +2264,8 @@ int zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
>>> * Use flush_needed to indicate whether the PMD entry
>>> * is present, instead of checking pmd_present() again.
>>> */
>>> - if (flush_needed && pmd_young(orig_pmd) &&
>>> - likely(vma_has_recency(vma)))
>>> + if (!exclusive_folio_of_dying_process(folio, vma) && flush_needed &&
Nit: I prefer to check 'flush_needed' first to make sure it is a present
pte. Otherwise look good to me.
>>> + pmd_young(orig_pmd) && likely(vma_has_recency(vma)))
>>> folio_mark_accessed(folio);
>>> }
>>>
>>> diff --git a/mm/internal.h b/mm/internal.h
>>> index 4e0ea83aaf1c..666de96a293d 100644
>>> --- a/mm/internal.h
>>> +++ b/mm/internal.h
>>> @@ -11,6 +11,7 @@
>>> #include <linux/khugepaged.h>
>>> #include <linux/mm.h>
>>> #include <linux/mm_inline.h>
>>> +#include <linux/oom.h>
>>> #include <linux/pagemap.h>
>>> #include <linux/pagewalk.h>
>>> #include <linux/rmap.h>
>>> @@ -130,6 +131,24 @@ static inline int folio_nr_pages_mapped(const struct folio *folio)
>>> return atomic_read(&folio->_nr_pages_mapped) & FOLIO_PAGES_MAPPED;
>>> }
>>>
>>> +/*
>>> + * Return true if a folio is exclusive and belongs to an exiting or
>>> + * oom-reaped process; otherwise, return false.
>>> + */
>>> +static inline bool exclusive_folio_of_dying_process(struct folio *folio,
>>> + struct vm_area_struct *vma)
>>> +{
>>> + if (folio_maybe_mapped_shared(folio))
>>> + return false;
>>> +
>>> + if (!atomic_read(&vma->vm_mm->mm_users))
>>> + return true;
>>> + if (check_stable_address_space(vma->vm_mm))
>>> + return true;
>>> +
>>> + return false;
>>> +}
>>> +
>>> /*
>>> * Retrieve the first entry of a folio based on a provided entry within the
>>> * folio. We cannot rely on folio->swap as there is no guarantee that it has
>>> diff --git a/mm/memory.c b/mm/memory.c
>>> index b9e8443aaa86..cab69275e473 100644
>>> --- a/mm/memory.c
>>> +++ b/mm/memory.c
>>> @@ -1515,7 +1515,14 @@ static __always_inline void zap_present_folio_ptes(struct mmu_gather *tlb,
>>> *force_flush = true;
>>> }
>>> }
>>> - if (pte_young(ptent) && likely(vma_has_recency(vma)))
>>> +
>>> + /*
>>> + * Skip marking exclusive file folios as accessed for processes that are
>>> + * exiting or have been reaped due to OOM. This prevents unnecessary
>>> + * promotion of folios that won't benefit the new process being launched.
>>> + */
>>> + if (!exclusive_folio_of_dying_process(folio, vma) && pte_young(ptent) &&
>>> + likely(vma_has_recency(vma)))
>>> folio_mark_accessed(folio);
>>> rss[mm_counter(folio)] -= nr;
>>> } else {
>>> --
>>> 2.39.3 (Apple Git-146)
>>
>>
>> --
>> Best Regards,
>> Yan, Zi
>
> Thanks
> Barry
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