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t=1789736096; bh=r0GY3Oko0Gbyya67DBjVH1KdCICd4o8CJaN93+aNccg=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=VZQJ928KoPiRfzqt8AG23Cmz8U28jicRXzuRF8TTlgkZ51YY0MvOnrtb4HBCVE9lg FMLU9ANEhkqUXnsLk7tfpYXFdukAvjd41OHOTRt9NiPlRl/OaKVN5qT3mpLejX9cmE b5f2PY32Vjc7SpYpQD/iG6YY3kpQk1OXTRPs5ow7vRATgGqh3QZEvY1u7GtvYbsQN8 Du1wtbDVw/bJ6Cs9GG4IbmNetnSmlfAeFu5JXntvlmyPRzvN6OEwVLh6i+bML7olFL YeZOjiehgW9qg19m+UL1UF00iWAULIRL85ZS2/hkIbbBa5xEb76gl6P5MlUGDc/Wfs 5U1nSsRvgs1Zw== Message-ID: <2c9f5d85-3396-4246-8179-3358a00ad223@kernel.org> Date: Fri, 18 Sep 2026 14:54:43 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 2/4] mm: allow shared folios to be promoted to a fast tier To: Zi Yan , Gregory Price , linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, kernel-team@meta.com, akpm@linux-foundation.org, ljs@kernel.org, liam@infradead.org, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, vschneid@redhat.com, kprateek.nayak@amd.com, baolin.wang@linux.alibaba.com, nico.pache@linux.dev, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, lance.yang@linux.dev, usama.arif@linux.dev, kas@kernel.org, matthew.brost@intel.com, joshua.hahnjy@gmail.com, rakie.kim@sk.com, byungchul@sk.com, ying.huang@linux.alibaba.com, apopple@nvidia.com, jannh@google.com, pfalcato@suse.de, osalvador@suse.de, hannes@cmpxchg.org, raghavendra.kt@amd.com, stable@vger.kernel.org References: <20260911001826.2109390-1-gourry@gourry.net> <20260911001826.2109390-3-gourry@gourry.net> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 636671A0003 X-Rspam-User: X-Stat-Signature: hjr5w5ft7yoje36bytpwon4acsirqbon X-HE-Tag: 1789736097-157244 X-HE-Meta: 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 QEICkDOO O+Zxz0oh5H6C4fWGb46bMdBX5TElm1g2F3n7HkG4aDQncYQMf5/xC7HZgUquJzlG+BXhUFzKh2agoOcQZDhK7DX2nO7sWMJGIJFwZH+4Tm4Boe3uqeWP0pnGwDOGPxEw2fAeka67uSRFXiKY/uoCHGM7xRNgJceOANAb8BvGWtXIQDruagK1ks3PD8vTnCRNynHOvTo9o8Qy/F++r1rpoI+xfqj6ZBGeEXDtSS2esoj22aeD/a/8+xmQosGSd/DZBddSbXKebDrVqgYrXI9r4KARWU5qd36OIFE0ALgqE2W/V6A3A6BQ3iKXh128w71A0D/UndNzFwEB+BWlx8P15oDAXsuRonKlYysrY+kdgG2kbGobMkL52Wz3P3b+0uNtUdwNvbk1oFz6FqjJnQKThHeZ7y2fTpR+vuRWG Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 9/17/26 19:49, Zi Yan wrote: > On Thu Sep 10, 2026 at 8:18 PM EDT, Gregory Price wrote: >> From: "Gregory Price (Meta)" >> >> NUMA balancing rejects shared copy-on-write folios and executable >> file folios mapped by multiple processes to avoid placement bouncing. >> These checks also block promotion from slow memory. >> >> Allow such folios to participate when moving from a slow tier to a fast >> tier. Keep the existing restrictions for ordinary placement. >> >> Fixes: c574bbe91703 ("NUMA balancing: optimize page placement for memory tiering system") >> Cc: stable@vger.kernel.org >> Assisted-by: LLM >> Signed-off-by: Gregory Price (Meta) >> --- >> mm/mempolicy.c | 8 ++++++-- >> mm/migrate.c | 6 ++++-- >> 2 files changed, 10 insertions(+), 4 deletions(-) >> >> diff --git a/mm/mempolicy.c b/mm/mempolicy.c >> index a082ccfa09ec..19b599bc2dd1 100644 >> --- a/mm/mempolicy.c >> +++ b/mm/mempolicy.c >> @@ -863,8 +863,12 @@ bool folio_can_map_prot_numa(struct folio *folio, struct vm_area_struct *vma, >> if (!folio || folio_is_zone_device(folio) || folio_test_ksm(folio)) >> return false; >> >> - /* Also skip shared copy-on-write folios */ >> - if (vma_is_cow_mapping(vma) && folio_maybe_mapped_shared(folio)) >> + /* >> + * Shared copy-on-write folios are poor NUMA placement candidates, but >> + * a hot folio on a slow tier still needs a hint fault for promotion. >> + */ >> + if (vma_is_cow_mapping(vma) && folio_maybe_mapped_shared(folio) && >> + !folio_use_access_time(folio)) >> return false; >> >> /* Folios are pinned and can't be migrated */ >> diff --git a/mm/migrate.c b/mm/migrate.c >> index a369d0c95c38..afd9c97d2389 100644 >> --- a/mm/migrate.c >> +++ b/mm/migrate.c >> @@ -2697,12 +2697,14 @@ int migrate_misplaced_folio_prepare(struct folio *folio, >> /* >> * Do not migrate file folios that are mapped in multiple >> * processes with execute permissions as they are probably >> - * shared libraries. >> + * shared libraries, unless this is a promotion from a slow tier. >> * >> * See folio_maybe_mapped_shared() on possible imprecision >> * when we cannot easily detect if a folio is shared. >> */ >> - if ((vma->vm_flags & VM_EXEC) && folio_maybe_mapped_shared(folio)) >> + if ((vma->vm_flags & VM_EXEC) && >> + folio_maybe_mapped_shared(folio) && >> + (!folio_use_access_time(folio) || !node_is_toptier(node))) >> return -EACCES; >> >> /* > > Should we rename folio_use_access_time() to folio_in_lowtier()? > Otherwise the code is really hard to understand. I just stumbled over that myself and I agree. > I admit that I > introduced folio_use_access_time() and it was probably because it > decides the use of folio_xchg_access_time() in > folio_can_map_prot_numa(). But in the other callsites, folio_in_lowtier() > makes more sense. We can just have an alias function if it makes the code easier to get. -- Cheers, David