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[2003:cb:c706:3100:19a8:d898:8e69:6aff]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-42158148f66sm22162595e9.32.2024.06.05.05.46.12 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 05 Jun 2024 05:46:13 -0700 (PDT) Message-ID: Date: Wed, 5 Jun 2024 14:46:12 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v6 2/3] mm/rmap: integrate PMD-mapped folio splitting into pagewalk loop To: Lance Yang , akpm@linux-foundation.org Cc: willy@infradead.org, sj@kernel.org, baolin.wang@linux.alibaba.com, maskray@google.com, ziy@nvidia.com, ryan.roberts@arm.com, 21cnbao@gmail.com, mhocko@suse.com, fengwei.yin@intel.com, zokeefe@google.com, shy828301@gmail.com, xiehuan09@gmail.com, libang.li@antgroup.com, wangkefeng.wang@huawei.com, songmuchun@bytedance.com, peterx@redhat.com, minchan@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20240521040244.48760-1-ioworker0@gmail.com> <20240521040244.48760-3-ioworker0@gmail.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 1772EA001B X-Rspam-User: X-Stat-Signature: 5fhm53oq9ntubaafnx577cjcj35d9sha X-HE-Tag: 1717591579-409203 X-HE-Meta: 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 nNoSh191 LIoeo9UCbqdE6UIVDWKIhNAghYH5HETZsjEpHLSlcGsfSpSaOGTr+pQrJ7H58D6Ttqxrkhi6YHALe7oTYXONawLqekshWlNsQQhxYjTRqK+klEPHkaNtjBA+TyW4k2Sg/QPdS7EsGKv8x+depjehyQ1BoyvQMO4+KfUtnj+W97+05Pq9hfX51ru5c3Ap4meSo5723wqwmoXmu70baBOQLdR2KB5oct4gx0FOiDkWLv3dj4M4PQVIkV6Witd3ynDbpt/P4nJeN9L4bhdZrFGFdXWU3TB1GS+PCiJqLYD6w6429Ya5MjUmMT85kA5W2yW4E6CMZyjrNGuYMXyKXAXWc/IhLfNou58+C9i7lg8buZXqL+s19MRoy7yum8OaFEbNAM7QleeI5x4Sc2+aaJTZs8wbdf055NthhxpG9P7Frf9PNcgwt4gcQddwkNdy1V9xQNvPIUhDMoC+3sNRfQQhvqPeBAGITl1Tnv8o5wqRzcBHdBeUBwdBcqBj/rq2+wccZh7ap6pqzxXYfWDnldqYdml7E/JVEZm2M3N8Czy9M2w8AU+MV+wzo6wN3tTLZ8m/S9fWzL11gCzqyZuzjAULhTkpj6qF4ATr4f7VGBPRFNn5MnmCnmfUjNqktzg== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 21.05.24 06:02, Lance Yang wrote: > In preparation for supporting try_to_unmap_one() to unmap PMD-mapped > folios, start the pagewalk first, then call split_huge_pmd_address() to > split the folio. > > Since TTU_SPLIT_HUGE_PMD will no longer perform immediately, we might > encounter a PMD-mapped THP missing the mlock in the VM_LOCKED range during > the page walk. It’s probably necessary to mlock this THP to prevent it from > being picked up during page reclaim. > > Suggested-by: David Hildenbrand > Suggested-by: Baolin Wang > Signed-off-by: Lance Yang > --- [...] again, sorry for the late review. > diff --git a/mm/rmap.c b/mm/rmap.c > index ddffa30c79fb..08a93347f283 100644 > --- a/mm/rmap.c > +++ b/mm/rmap.c > @@ -1640,9 +1640,6 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma, > if (flags & TTU_SYNC) > pvmw.flags = PVMW_SYNC; > > - if (flags & TTU_SPLIT_HUGE_PMD) > - split_huge_pmd_address(vma, address, false, folio); > - > /* > * For THP, we have to assume the worse case ie pmd for invalidation. > * For hugetlb, it could be much worse if we need to do pud > @@ -1668,20 +1665,35 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma, > mmu_notifier_invalidate_range_start(&range); > > while (page_vma_mapped_walk(&pvmw)) { > - /* Unexpected PMD-mapped THP? */ > - VM_BUG_ON_FOLIO(!pvmw.pte, folio); > - > /* > * If the folio is in an mlock()d vma, we must not swap it out. > */ > if (!(flags & TTU_IGNORE_MLOCK) && > (vma->vm_flags & VM_LOCKED)) { > /* Restore the mlock which got missed */ > - if (!folio_test_large(folio)) > + if (!folio_test_large(folio) || > + (!pvmw.pte && (flags & TTU_SPLIT_HUGE_PMD))) > mlock_vma_folio(folio, vma); Can you elaborate why you think this would be required? If we would have performed the split_huge_pmd_address() beforehand, we would still be left with a large folio, no? > goto walk_done_err; > } > > + if (!pvmw.pte && (flags & TTU_SPLIT_HUGE_PMD)) { > + /* > + * We temporarily have to drop the PTL and start once > + * again from that now-PTE-mapped page table. > + */ > + split_huge_pmd_locked(vma, range.start, pvmw.pmd, false, > + folio); Using range.start here is a bit weird. Wouldn't this be pvmw.address? [did not check] > + pvmw.pmd = NULL; > + spin_unlock(pvmw.ptl); > + pvmw.ptl = NULL; Would we want a page_vma_mapped_walk_restart() that is exactly for that purpose? > + flags &= ~TTU_SPLIT_HUGE_PMD; > + continue; > + } > + > + /* Unexpected PMD-mapped THP? */ > + VM_BUG_ON_FOLIO(!pvmw.pte, folio); -- Cheers, David / dhildenb