kernel/linux.git/include/linux/khugepaged.h, branch v6.6.131

mm: vmscan: split khugepaged stats from direct reclaim stats

2022-11-30T23:58:41+00:00

Direct reclaim stats are useful for identifying a potential source for application latency, as well as spotting issues with kswapd. However, khugepaged currently distorts the picture: as a kernel thread it doesn't impose allocation latencies on userspace, and it explicitly opts out of kswapd reclaim. Its activity showing up in the direct reclaim stats is misleading. Counting it as kswapd reclaim could also cause confusion when trying to understand actual kswapd behavior. Break out khugepaged from the direct reclaim counters into new pgsteal_khugepaged, pgdemote_khugepaged, pgscan_khugepaged counters. Test with a huge executable (CONFIG_READ_ONLY_THP_FOR_FS): pgsteal_kswapd 1342185 pgsteal_direct 0 pgsteal_khugepaged 3623 pgscan_kswapd 1345025 pgscan_direct 0 pgscan_khugepaged 3623 Link: https://lkml.kernel.org/r/20221026180133.377671-1-hannes@cmpxchg.org Signed-off-by: Johannes Weiner Reported-by: Eric Bergen Cc: Matthew Wilcox (Oracle) Cc: Yang Shi Cc: Yosry Ahmed Signed-off-by: Andrew Morton

mm/madvise: add file and shmem support to MADV_COLLAPSE

2022-10-03T21:03:33+00:00

Add support for MADV_COLLAPSE to collapse shmem-backed and file-backed memory into THPs (requires CONFIG_READ_ONLY_THP_FOR_FS=y). On success, the backing memory will be a hugepage. For the memory range and process provided, the page tables will synchronously have a huge pmd installed, mapping the THP. Other mappings of the file extent mapped by the memory range may be added to a set of entries that khugepaged will later process and attempt update their page tables to map the THP by a pmd. This functionality unlocks two important uses: (1) Immediately back executable text by THPs. Current support provided by CONFIG_READ_ONLY_THP_FOR_FS may take a long time on a large system which might impair services from serving at their full rated load after (re)starting. Tricks like mremap(2)'ing text onto anonymous memory to immediately realize iTLB performance prevents page sharing and demand paging, both of which increase steady state memory footprint. Now, we can have the best of both worlds: Peak upfront performance and lower RAM footprints. (2) userfaultfd-based live migration of virtual machines satisfy UFFD faults by fetching native-sized pages over the network (to avoid latency of transferring an entire hugepage). However, after guest memory has been fully copied to the new host, MADV_COLLAPSE can be used to immediately increase guest performance. Since khugepaged is single threaded, this change now introduces possibility of collapse contexts racing in file collapse path. There a important few places to consider: (1) hpage_collapse_scan_file(), when we xas_pause() and drop RCU. We could have the memory collapsed out from under us, but the next xas_for_each() iteration will correctly pick up the hugepage. The hugepage might not be up to date (insofar as copying of small page contents might not have completed - the page still may be locked), but regardless what small page index we were iterating over, we'll find the hugepage and identify it as a suitably aligned compound page of order HPAGE_PMD_ORDER. In khugepaged path, we locklessly check the value of the pmd, and only add it to deferred collapse array if we find pmd mapping pte table. This is fine, since other values that could have raced in right afterwards denote failure, or that the memory was successfully collapsed, so we don't need further processing. In madvise path, we'll take mmap_lock() in write to serialize against page table updates and will know what to do based on the true value of the pmd: recheck all ptes if we point to a pte table, directly install the pmd, if the pmd has been cleared, but memory not yet faulted, or nothing at all if we find a huge pmd. It's worth putting emphasis here on how we treat the none pmd here. If khugepaged has processed this mm's page tables already, it will have left the pmd cleared (ready for refault by the process). Depending on the VMA flags and sysfs settings, amount of RAM on the machine, and the current load, could be a relatively common occurrence - and as such is one we'd like to handle successfully in MADV_COLLAPSE. When we see the none pmd in collapse_pte_mapped_thp(), we've locked mmap_lock in write and checked (a) huepaged_vma_check() to see if the backing memory is appropriate still, along with VMA sizing and appropriate hugepage alignment within the file, and (b) we've found a hugepage head of order HPAGE_PMD_ORDER at the offset in the file mapped by our hugepage-aligned virtual address. Even though the common-case is likely race with khugepaged, given these checks (regardless how we got here - we could be operating on a completely different file than originally checked in hpage_collapse_scan_file() for all we know) it should be safe to directly make the pmd a huge pmd pointing to this hugepage. (2) collapse_file() is mostly serialized on the same file extent by lock sequence: | lock hupepage | lock mapping->i_pages | lock 1st page | unlock mapping->i_pages | | lock mapping->i_pages | page_ref_freeze(3) | xas_store(hugepage) | unlock mapping->i_pages | page_ref_unfreeze(1) | unlock 1st page V unlock hugepage Once a context (who already has their fresh hugepage locked) locks mapping->i_pages exclusively, it will hold said lock until it locks the first page, and it will hold that lock until the after the hugepage has been added to the page cache (and will unlock the hugepage after page table update, though that isn't important here). A racing context that loses the race for mapping->i_pages will then lose the race to locking the first page. Here - depending on how far the other racing context has gotten - we might find the new hugepage (in which case we'll exit cleanly when we check PageTransCompound()), or we'll find the "old" 1st small page (in which we'll exit cleanly when we discover unexpected refcount of 2 after isolate_lru_page()). This is assuming we are able to successfully lock the page we find - in shmem path, we could just fail the trylock and exit cleanly anyways. Failure path in collapse_file() is similar: once we hold lock on 1st small page, we are serialized against other collapse contexts. Before the 1st small page is unlocked, we add it back to the pagecache and unfreeze the refcount appropriately. Contexts who lost the race to the 1st small page will then find the same 1st small page with the correct refcount and will be able to proceed. [zokeefe@google.com: don't check pmd value twice in collapse_pte_mapped_thp()] Link: https://lkml.kernel.org/r/20220927033854.477018-1-zokeefe@google.com [shy828301@gmail.com: Delete hugepage_vma_revalidate_anon(), remove check for multi-add in khugepaged_add_pte_mapped_thp()] Link: https://lore.kernel.org/linux-mm/CAHbLzkrtpM=ic7cYAHcqkubah5VTR8N5=k5RT8MTvv5rN1Y91w@mail.gmail.com/ Link: https://lkml.kernel.org/r/20220907144521.3115321-4-zokeefe@google.com Link: https://lkml.kernel.org/r/20220922224046.1143204-4-zokeefe@google.com Signed-off-by: Zach O'Keefe Cc: Axel Rasmussen Cc: Chris Kennelly Cc: David Hildenbrand Cc: David Rientjes Cc: Hugh Dickins Cc: James Houghton Cc: "Kirill A. Shutemov" Cc: Matthew Wilcox Cc: Miaohe Lin Cc: Minchan Kim Cc: Pasha Tatashin Cc: Peter Xu Cc: Rongwei Wang Cc: SeongJae Park Cc: Song Liu Cc: Vlastimil Babka Cc: Yang Shi Signed-off-by: Andrew Morton

mm: khugepaged: reorg some khugepaged helpers

2022-07-18T00:14:33+00:00

The khugepaged_{enabled|always|req_madv} are not khugepaged only anymore, move them to huge_mm.h and rename to hugepage_flags_xxx, and remove khugepaged_req_madv due to no users. Also move khugepaged_defrag to khugepaged.c since its only caller is in that file, it doesn't have to be in a header file. Link: https://lkml.kernel.org/r/20220616174840.1202070-7-shy828301@gmail.com Signed-off-by: Yang Shi Reviewed-by: Zach O'Keefe Cc: Kirill A. Shutemov Cc: Matthew Wilcox Cc: Miaohe Lin Cc: Vlastimil Babka Signed-off-by: Andrew Morton

mm: thp: kill transparent_hugepage_active()

2022-07-18T00:14:33+00:00

The transparent_hugepage_active() was introduced to show THP eligibility bit in smaps in proc, smaps is the only user. But it actually does the similar check as hugepage_vma_check() which is used by khugepaged. We definitely don't have to maintain two similar checks, so kill transparent_hugepage_active(). This patch also fixed the wrong behavior for VM_NO_KHUGEPAGED vmas. Also move hugepage_vma_check() to huge_memory.c and huge_mm.h since it is not only for khugepaged anymore. [akpm@linux-foundation.org: check vma->vm_mm, per Zach] [akpm@linux-foundation.org: add comment to vdso check] Link: https://lkml.kernel.org/r/20220616174840.1202070-5-shy828301@gmail.com Signed-off-by: Yang Shi Reviewed-by: Zach O'Keefe Cc: Kirill A. Shutemov Cc: Matthew Wilcox Cc: Miaohe Lin Cc: Vlastimil Babka Signed-off-by: Andrew Morton

mm: thp: consolidate vma size check to transhuge_vma_suitable

2022-07-18T00:14:32+00:00

There are couple of places that check whether the vma size is ok for THP or whether address fits, they are open coded and duplicate, use transhuge_vma_suitable() to do the job by passing in (vma->end - HPAGE_PMD_SIZE). Move vma size check into hugepage_vma_check(). This will make khugepaged_enter() is as same as khugepaged_enter_vma(). There is just one caller for khugepaged_enter(), replace it to khugepaged_enter_vma() and remove khugepaged_enter(). Link: https://lkml.kernel.org/r/20220616174840.1202070-3-shy828301@gmail.com Signed-off-by: Yang Shi Reviewed-by: Zach O'Keefe Cc: Kirill A. Shutemov Cc: Matthew Wilcox Cc: Miaohe Lin Cc: Vlastimil Babka Signed-off-by: Andrew Morton

mm: khugepaged: introduce khugepaged_enter_vma() helper

2022-05-19T21:08:50+00:00

The khugepaged_enter_vma_merge() actually does as the same thing as the khugepaged_enter() section called by shmem_mmap(), so consolidate them into one helper and rename it to khugepaged_enter_vma(). Link: https://lkml.kernel.org/r/20220510203222.24246-8-shy828301@gmail.com Signed-off-by: Yang Shi Acked-by: Vlastmil Babka Cc: Kirill A. Shutemov Cc: Matthew Wilcox (Oracle) Cc: Miaohe Lin Cc: Rik van Riel Cc: Song Liu Cc: Song Liu Cc: Theodore Ts'o Cc: Zi Yan Signed-off-by: Andrew Morton

mm: khugepaged: make hugepage_vma_check() non-static

2022-05-19T21:08:49+00:00

The hugepage_vma_check() could be reused by khugepaged_enter() and khugepaged_enter_vma_merge(), but it is static in khugepaged.c. Make it non-static and declare it in khugepaged.h. Link: https://lkml.kernel.org/r/20220510203222.24246-7-shy828301@gmail.com Signed-off-by: Yang Shi Suggested-by: Vlastimil Babka Cc: Kirill A. Shutemov Cc: Matthew Wilcox (Oracle) Cc: Miaohe Lin Cc: Rik van Riel Cc: Song Liu Cc: Song Liu Cc: Theodore Ts'o Cc: Zi Yan Signed-off-by: Andrew Morton

mm: khugepaged: make khugepaged_enter() void function

2022-05-19T21:08:49+00:00

The most callers of khugepaged_enter() don't care about the return value. Only dup_mmap(), anonymous THP page fault and MADV_HUGEPAGE handle the error by returning -ENOMEM. Actually it is not harmful for them to ignore the error case either. It also sounds overkilling to fail fork() and page fault early due to khugepaged_enter() error, and MADV_HUGEPAGE does set VM_HUGEPAGE flag regardless of the error. Link: https://lkml.kernel.org/r/20220510203222.24246-6-shy828301@gmail.com Signed-off-by: Yang Shi Acked-by: Song Liu Acked-by: Vlastmil Babka Cc: Kirill A. Shutemov Cc: Matthew Wilcox (Oracle) Cc: Miaohe Lin Cc: Rik van Riel Cc: Song Liu Cc: Theodore Ts'o Cc: Zi Yan Signed-off-by: Andrew Morton

mm,thp,shmem: make khugepaged obey tmpfs mount flags

2021-02-26T17:40:59+00:00

Currently if thp enabled=[madvise], mounting a tmpfs filesystem with huge=always and mmapping files from that tmpfs does not result in khugepaged collapsing those mappings, despite the mount flag indicating that it should. Fix that by breaking up the blocks of tests in hugepage_vma_check a little bit, and testing things in the correct order. Link: https://lkml.kernel.org/r/20201124194925.623931-4-riel@surriel.com Fixes: c2231020ea7b ("mm: thp: register mm for khugepaged when merging vma for shmem") Signed-off-by: Rik van Riel Cc: Andrea Arcangeli Cc: Hugh Dickins Cc: Matthew Wilcox (Oracle) Cc: Mel Gorman Cc: Michal Hocko Cc: Vlastimil Babka Cc: Xu Yu Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm: khugepaged: recalculate min_free_kbytes after memory hotplug as expected by khugepaged

2020-10-11T17:31:11+00:00

When memory is hotplug added or removed the min_free_kbytes should be recalculated based on what is expected by khugepaged. Currently after hotplug, min_free_kbytes will be set to a lower default and higher default set when THP enabled is lost. This change restores min_free_kbytes as expected for THP consumers. [vijayb@linux.microsoft.com: v5] Link: https://lkml.kernel.org/r/1601398153-5517-1-git-send-email-vijayb@linux.microsoft.com Fixes: f000565adb77 ("thp: set recommended min free kbytes") Signed-off-by: Vijay Balakrishna Signed-off-by: Andrew Morton Reviewed-by: Pavel Tatashin Acked-by: Michal Hocko Cc: Allen Pais Cc: Andrea Arcangeli Cc: "Kirill A. Shutemov" Cc: Oleg Nesterov Cc: Song Liu Cc: Link: https://lkml.kernel.org/r/1600305709-2319-2-git-send-email-vijayb@linux.microsoft.com Link: https://lkml.kernel.org/r/1600204258-13683-1-git-send-email-vijayb@linux.microsoft.com Signed-off-by: Linus Torvalds