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[2003:cb:c740:2200:95d8:cbf4:fffd:7f81]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3609aa60a59sm1739171f8f.84.2024.06.17.11.04.43 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 17 Jun 2024 11:04:44 -0700 (PDT) Message-ID: Date: Mon, 17 Jun 2024 20:04:42 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v8 3/3] mm/vmscan: avoid split lazyfree THP during shrink_folio_list() 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: <20240614015138.31461-1-ioworker0@gmail.com> <20240614015138.31461-4-ioworker0@gmail.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: AF4A880008 X-Stat-Signature: k48whj54bhs5c7c83m14jqtxifyac7h8 X-Rspamd-Server: rspam09 X-Rspam-User: X-HE-Tag: 1718647490-516473 X-HE-Meta: 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 Kh3mOFBO 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 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: Sorry for taking so long to review ... getting there. Mostly nits. > @@ -497,6 +499,13 @@ static inline void split_huge_pmd_locked(struct vm_area_struct *vma, > unsigned long address, pmd_t *pmd, > bool freeze, struct folio *folio) {} > > +static inline bool unmap_huge_pmd_locked(struct vm_area_struct *vma, > + unsigned long addr, pmd_t *pmdp, > + struct folio *folio) > +{ > + return false; > +} > + > #define split_huge_pud(__vma, __pmd, __address) \ > do { } while (0) > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index e766d3f3a302..425374ae06ed 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -2688,6 +2688,82 @@ static void unmap_folio(struct folio *folio) > try_to_unmap_flush(); > } > > +static bool __discard_anon_folio_pmd_locked(struct vm_area_struct *vma, > + unsigned long addr, pmd_t *pmdp, > + struct folio *folio) > +{ > + VM_WARN_ON_FOLIO(folio_test_swapbacked(folio), folio); > + VM_WARN_ON_FOLIO(!folio_test_anon(folio), folio); I would drop these (that's exactly what the single caller checks). In any case don't place them above the variable declaration ;) > + > + struct mm_struct *mm = vma->vm_mm; > + int ref_count, map_count; > + pmd_t orig_pmd = *pmdp; > + struct page *page; > + > + if (unlikely(!pmd_present(orig_pmd) || !pmd_trans_huge(orig_pmd))) > + return false; > + > + page = pmd_page(orig_pmd); > + if (unlikely(page_folio(page) != folio)) > + return false; I'm curious, how could that happen? And how could it happen that we have !pmd_trans_huge() ? Didn't rmap walking code make sure that this PMD maps the folio already, and we are holding the PTL? > + > + if (folio_test_dirty(folio) || pmd_dirty(orig_pmd)) > + return false; > + > + orig_pmd = pmdp_huge_clear_flush(vma, addr, pmdp); > + > + /* > + * Syncing against concurrent GUP-fast: > + * - clear PMD; barrier; read refcount > + * - inc refcount; barrier; read PMD > + */ > + smp_mb(); > + > + ref_count = folio_ref_count(folio); > + map_count = folio_mapcount(folio); > + > + /* > + * Order reads for folio refcount and dirty flag > + * (see comments in __remove_mapping()). > + */ > + smp_rmb(); > + > + /* > + * If the folio or its PMD is redirtied at this point, or if there > + * are unexpected references, we will give up to discard this folio > + * and remap it. > + * > + * The only folio refs must be one from isolation plus the rmap(s). > + */ > + if (folio_test_dirty(folio) || pmd_dirty(orig_pmd) || > + ref_count != map_count + 1) { > + set_pmd_at(mm, addr, pmdp, orig_pmd); > + return false; > + } > + > + folio_remove_rmap_pmd(folio, page, vma); > + zap_deposited_table(mm, pmdp); > + add_mm_counter(mm, MM_ANONPAGES, -HPAGE_PMD_NR); > + if (vma->vm_flags & VM_LOCKED) > + mlock_drain_local(); > + folio_put(folio); > + > + return true; > +} > + > +bool unmap_huge_pmd_locked(struct vm_area_struct *vma, unsigned long addr, > + pmd_t *pmdp, struct folio *folio) > +{ > + VM_WARN_ON_FOLIO(!folio_test_pmd_mappable(folio), folio); > + VM_WARN_ON_FOLIO(!folio_test_locked(folio), folio); > + VM_WARN_ON_ONCE(!IS_ALIGNED(addr, HPAGE_PMD_SIZE)); > + > + if (folio_test_anon(folio) && !folio_test_swapbacked(folio)) > + return __discard_anon_folio_pmd_locked(vma, addr, pmdp, folio); > + > + return false; > +} > + > static void remap_page(struct folio *folio, unsigned long nr) > { > int i = 0; > diff --git a/mm/rmap.c b/mm/rmap.c > index dacf24bc82f0..7d97806f74cd 100644 > --- a/mm/rmap.c > +++ b/mm/rmap.c > @@ -1678,16 +1678,23 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma, > goto walk_abort; > } > > - 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, pvmw.address, pvmw.pmd, > - false, folio); > - flags &= ~TTU_SPLIT_HUGE_PMD; > - page_vma_mapped_walk_restart(&pvmw); > - continue; > + if (!pvmw.pte) { > + if (unmap_huge_pmd_locked(vma, pvmw.address, pvmw.pmd, > + folio)) > + goto walk_done; > + > + if (flags & TTU_SPLIT_HUGE_PMD) { > + /* > + * We temporarily have to drop the PTL and start > + * once again from that now-PTE-mapped page > + * table. Nit: it's not a PTE-mapped page table. Maybe "... restart so we can process the PTE-mapped THP." > } > > /* Unexpected PMD-mapped THP? */ Nothing else jumped at me :) -- Cheers, David / dhildenb