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(p200300cbc7045d00d8c2fbf6a608957a.dip0.t-ipconnect.de. [2003:cb:c704:5d00:d8c2:fbf6:a608:957a]) by smtp.gmail.com with ESMTPSA id p4-20020a1c5444000000b00391ca5976c8sm14672796wmi.0.2022.04.19.09.46.43 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 19 Apr 2022 09:46:44 -0700 (PDT) Message-ID: <219bd2d0-92ef-bcac-458a-0df6190fa387@redhat.com> Date: Tue, 19 Apr 2022 18:46:43 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.6.2 Subject: Re: [PATCH v3 12/16] mm: remember exclusively mapped anonymous pages with PG_anon_exclusive Content-Language: en-US To: Vlastimil Babka , linux-kernel@vger.kernel.org Cc: Andrew Morton , Hugh Dickins , Linus Torvalds , David Rientjes , Shakeel Butt , John Hubbard , Jason Gunthorpe , Mike Kravetz , Mike Rapoport , Yang Shi , "Kirill A . Shutemov" , Matthew Wilcox , Jann Horn , Michal Hocko , Nadav Amit , Rik van Riel , Roman Gushchin , Andrea Arcangeli , Peter Xu , Donald Dutile , Christoph Hellwig , Oleg Nesterov , Jan Kara , Liang Zhang , Pedro Gomes , Oded Gabbay , linux-mm@kvack.org References: <20220329160440.193848-1-david@redhat.com> <20220329160440.193848-13-david@redhat.com> <012e3889-563b-e7fc-c2e3-e7a6373a55ac@suse.cz> <2ae0a409-3d6d-9f6a-09e8-2f6867a4069a@redhat.com> <5fc7d007-e59b-de8d-4d88-3f1b5adfa95b@suse.cz> From: David Hildenbrand Organization: Red Hat In-Reply-To: <5fc7d007-e59b-de8d-4d88-3f1b5adfa95b@suse.cz> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 13.04.22 20:28, Vlastimil Babka wrote: > On 4/13/22 18:39, David Hildenbrand wrote: >>>> @@ -3035,10 +3083,19 @@ void set_pmd_migration_entry(struct page_vma_mapped_walk *pvmw, >>>> >>>> flush_cache_range(vma, address, address + HPAGE_PMD_SIZE); >>>> pmdval = pmdp_invalidate(vma, address, pvmw->pmd); >>>> + >>>> + anon_exclusive = PageAnon(page) && PageAnonExclusive(page); >>>> + if (anon_exclusive && page_try_share_anon_rmap(page)) { >>>> + set_pmd_at(mm, address, pvmw->pmd, pmdval); >>>> + return; >>> >>> I am admittedly not too familiar with this code, but looks like this means >>> we fail to migrate the THP, right? But we don't seem to be telling the >>> caller, which is try_to_migrate_one(), so it will continue and not terminate >>> the walk and return false? >> >> Right, we're not returning "false". Returning "false" would be an >> optimization to make rmap_walk_anon() fail faster. > > Ah right, that's what I missed, it's an optimization and we will realize > elsewhere afterwards that the page has still mappings and we can't migrate... I'll include that patch in v4 (to be tested): >From 08fb0e45404e3d0f85c2ad23a473e95053396376 Mon Sep 17 00:00:00 2001 From: David Hildenbrand Date: Tue, 19 Apr 2022 18:39:23 +0200 Subject: [PATCH] mm/rmap: fail try_to_migrate() early when setting a PMD migration entry fails Let's fail right away in case we cannot clear PG_anon_exclusive because the anon THP may be pinned. Right now, we continue trying to install migration entries and the caller of try_to_migrate() will realize that the page is still mapped and has to restore the migration entries. Let's just fail fast just like for PTE migration entries. Suggested-by: Vlastimil Babka Signed-off-by: David Hildenbrand --- include/linux/swapops.h | 4 ++-- mm/huge_memory.c | 8 +++++--- mm/rmap.c | 6 +++++- 3 files changed, 12 insertions(+), 6 deletions(-) diff --git a/include/linux/swapops.h b/include/linux/swapops.h index 06280fc1c99b..8b6e4cd1fab8 100644 --- a/include/linux/swapops.h +++ b/include/linux/swapops.h @@ -299,7 +299,7 @@ static inline bool is_pfn_swap_entry(swp_entry_t entry) struct page_vma_mapped_walk; #ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION -extern void set_pmd_migration_entry(struct page_vma_mapped_walk *pvmw, +extern int set_pmd_migration_entry(struct page_vma_mapped_walk *pvmw, struct page *page); extern void remove_migration_pmd(struct page_vma_mapped_walk *pvmw, @@ -332,7 +332,7 @@ static inline int is_pmd_migration_entry(pmd_t pmd) return !pmd_present(pmd) && is_migration_entry(pmd_to_swp_entry(pmd)); } #else -static inline void set_pmd_migration_entry(struct page_vma_mapped_walk *pvmw, +static inline int set_pmd_migration_entry(struct page_vma_mapped_walk *pvmw, struct page *page) { BUILD_BUG(); diff --git a/mm/huge_memory.c b/mm/huge_memory.c index c7ac1b462543..390f22334ee9 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -3080,7 +3080,7 @@ late_initcall(split_huge_pages_debugfs); #endif #ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION -void set_pmd_migration_entry(struct page_vma_mapped_walk *pvmw, +int set_pmd_migration_entry(struct page_vma_mapped_walk *pvmw, struct page *page) { struct vm_area_struct *vma = pvmw->vma; @@ -3092,7 +3092,7 @@ void set_pmd_migration_entry(struct page_vma_mapped_walk *pvmw, pmd_t pmdswp; if (!(pvmw->pmd && !pvmw->pte)) - return; + return 0; flush_cache_range(vma, address, address + HPAGE_PMD_SIZE); pmdval = pmdp_invalidate(vma, address, pvmw->pmd); @@ -3100,7 +3100,7 @@ void set_pmd_migration_entry(struct page_vma_mapped_walk *pvmw, anon_exclusive = PageAnon(page) && PageAnonExclusive(page); if (anon_exclusive && page_try_share_anon_rmap(page)) { set_pmd_at(mm, address, pvmw->pmd, pmdval); - return; + return -EBUSY; } if (pmd_dirty(pmdval)) @@ -3118,6 +3118,8 @@ void set_pmd_migration_entry(struct page_vma_mapped_walk *pvmw, page_remove_rmap(page, vma, true); put_page(page); trace_set_migration_pmd(address, pmd_val(pmdswp)); + + return 0; } void remove_migration_pmd(struct page_vma_mapped_walk *pvmw, struct page *new) diff --git a/mm/rmap.c b/mm/rmap.c index 00418faaf4ce..68c2f61bf212 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -1814,7 +1814,11 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma, VM_BUG_ON_FOLIO(folio_test_hugetlb(folio) || !folio_test_pmd_mappable(folio), folio); - set_pmd_migration_entry(&pvmw, subpage); + if (set_pmd_migration_entry(&pvmw, subpage)) { + ret = false; + page_vma_mapped_walk_done(&pvmw); + break; + } continue; } #endif -- 2.35.1 -- Thanks, David / dhildenb