kernel/lib/xarray.c, branch linux-6.15.y

mm/filemap: use xas_try_split() in __filemap_add_folio()

2025-03-18T05:07:01Z

Patch series "Minimize xa_node allocation during xarry split", v3. When splitting a multi-index entry in XArray from order-n to order-m, existing xas_split_alloc()+xas_split() approach requires 2^(n % XA_CHUNK_SHIFT) xa_node allocations. But its callers, __filemap_add_folio() and shmem_split_large_entry(), use at most 1 xa_node. To minimize xa_node allocation and remove the limitation of no split from order-12 (or above) to order-0 (or anything between 0 and 5)[1], xas_try_split() was added[2], which allocates (n / XA_CHUNK_SHIFT - m / XA_CHUNK_SHIFT) xa_node. It is used for non-uniform folio split, but can be used by __filemap_add_folio() and shmem_split_large_entry(). xas_split_alloc() and xas_split() split an order-9 to order-0: --------------------------------- | | | | | | | | | | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | | | | | | | | | | --------------------------------- | | | | ------- --- --- ------- | | ... | | V V V V ----------- ----------- ----------- ----------- | xa_node | | xa_node | ... | xa_node | | xa_node | ----------- ----------- ----------- ----------- xas_try_split() splits an order-9 to order-0: --------------------------------- | | | | | | | | | | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | | | | | | | | | | --------------------------------- | | V ----------- | xa_node | ----------- xas_try_split() is designed to be called iteratively with n = m + 1. xas_try_split_mini_order() is added to minmize the number of calls to xas_try_split() by telling the caller the next minimal order to split to instead of n - 1. Splitting order-n to order-m when m= l * XA_CHUNK_SHIFT does not require xa_node allocation and requires 1 xa_node when n=l * XA_CHUNK_SHIFT and m = n - 1, so it is OK to use xas_try_split() with n > m + 1 when no new xa_node is needed. xfstests quick group test passed on xfs and tmpfs. [1] https://lore.kernel.org/linux-mm/Z6YX3RznGLUD07Ao@casper.infradead.org/ [2] https://lore.kernel.org/linux-mm/20250226210032.2044041-1-ziy@nvidia.com/ This patch (of 2): During __filemap_add_folio(), a shadow entry is covering n slots and a folio covers m slots with m < n is to be added. Instead of splitting all n slots, only the m slots covered by the folio need to be split and the remaining n-m shadow entries can be retained with orders ranging from m to n-1. This method only requires (n/XA_CHUNK_SHIFT) - (m/XA_CHUNK_SHIFT) new xa_nodes instead of (n % XA_CHUNK_SHIFT) * ((n/XA_CHUNK_SHIFT) - (m/XA_CHUNK_SHIFT)) new xa_nodes, compared to the original xas_split_alloc() + xas_split() one. For example, to insert an order-0 folio when an order-9 shadow entry is present (assuming XA_CHUNK_SHIFT is 6), 1 xa_node is needed instead of 8. xas_try_split_min_order() is introduced to reduce the number of calls to xas_try_split() during split. Link: https://lkml.kernel.org/r/20250314222113.711703-1-ziy@nvidia.com Link: https://lkml.kernel.org/r/20250314222113.711703-2-ziy@nvidia.com Signed-off-by: Zi Yan Cc: Baolin Wang Cc: Hugh Dickins Cc: Kairui Song Cc: Miaohe Lin Cc: Mattew Wilcox Cc: David Hildenbrand Cc: John Hubbard Cc: Kefeng Wang Cc: Kirill A. Shuemov Cc: Ryan Roberts Cc: Yang Shi Cc: Yu Zhao Signed-off-by: Andrew Morton

xarray: add xas_try_split() to split a multi-index entry

2025-03-18T05:06:59Z

Patch series "Buddy allocator like (or non-uniform) folio split", v10. This patchset adds a new buddy allocator like (or non-uniform) large folio split from a order-n folio to order-m with m < n. It reduces 1. the total number of after-split folios from 2^(n-m) to n-m+1; 2. the amount of memory needed for multi-index xarray split from 2^(n/6-m/6) to n/6-m/6, assuming XA_CHUNK_SHIFT=6; 3. keep more large folios after a split from all order-m folios to order-(n-1) to order-m folios. For example, to split an order-9 to order-0, folio split generates 10 (or 11 for anonymous memory) folios instead of 512, allocates 1 xa_node instead of 8, and leaves 1 order-8, 1 order-7, ..., 1 order-1 and 2 order-0 folios (or 4 order-0 for anonymous memory) instead of 512 order-0 folios. Instead of duplicating existing split_huge_page*() code, __folio_split() is introduced as the shared backend code for both split_huge_page_to_list_to_order() and folio_split(). __folio_split() can support both uniform split and buddy allocator like (or non-uniform) split. All existing split_huge_page*() users can be gradually converted to use folio_split() if possible. In this patchset, I converted truncate_inode_partial_folio() to use folio_split(). xfstests quick group passed for both tmpfs and xfs. I also semi-replicated Hugh's test[12] and ran it without any issue for almost 24 hours. This patch (of 8): A preparation patch for non-uniform folio split, which always split a folio into half iteratively, and minimal xarray entry split. Currently, xas_split_alloc() and xas_split() always split all slots from a multi-index entry. They cost the same number of xa_node as the to-be-split slots. For example, to split an order-9 entry, which takes 2^(9-6)=8 slots, assuming XA_CHUNK_SHIFT is 6 (!CONFIG_BASE_SMALL), 8 xa_node are needed. Instead xas_try_split() is intended to be used iteratively to split the order-9 entry into 2 order-8 entries, then split one order-8 entry, based on the given index, to 2 order-7 entries, ..., and split one order-1 entry to 2 order-0 entries. When splitting the order-6 entry and a new xa_node is needed, xas_try_split() will try to allocate one if possible. As a result, xas_try_split() would only need 1 xa_node instead of 8. When a new xa_node is needed during the split, xas_try_split() can try to allocate one but no more. -ENOMEM will be return if a node cannot be allocated. -EINVAL will be return if a sibling node is split or cascade split happens, where two or more new nodes are needed, and these are not supported by xas_try_split(). xas_split_alloc() and xas_split() split an order-9 to order-0: --------------------------------- | | | | | | | | | | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | | | | | | | | | | --------------------------------- | | | | ------- --- --- ------- | | ... | | V V V V ----------- ----------- ----------- ----------- | xa_node | | xa_node | ... | xa_node | | xa_node | ----------- ----------- ----------- ----------- xas_try_split() splits an order-9 to order-0: --------------------------------- | | | | | | | | | | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | | | | | | | | | | --------------------------------- | | V ----------- | xa_node | ----------- Link: https://lkml.kernel.org/r/20250307174001.242794-1-ziy@nvidia.com Link: https://lkml.kernel.org/r/20250307174001.242794-2-ziy@nvidia.com Signed-off-by: Zi Yan Cc: Baolin Wang Cc: David Hildenbrand Cc: Hugh Dickins Cc: John Hubbard Cc: Kefeng Wang Cc: Kirill A. Shuemov Cc: Miaohe Lin Cc: Matthew Wilcox Cc: Ryan Roberts Cc: Yang Shi Cc: Yu Zhao Cc: Zi Yan Cc: Kairui Song Signed-off-by: Andrew Morton

Xarray: use xa_mark_t in xas_squash_marks() to keep code consistent

2025-01-25T06:47:28Z

Besides xas_squash_marks(), all functions use xa_mark_t type to iterate all possible marks. Use xa_mark_t in xas_squash_marks() to keep code consistent. Link: https://lkml.kernel.org/r/20241213122523.12764-6-shikemeng@huaweicloud.com Signed-off-by: Kemeng Shi Cc: Mattew Wilcox Signed-off-by: Andrew Morton

Xarray: remove repeat check in xas_squash_marks()

2025-01-25T06:47:27Z

Caller of xas_squash_marks() has ensured xas->xa_sibs is non-zero. Just remove repeat check of xas->xa_sibs in xas_squash_marks(). Link: https://lkml.kernel.org/r/20241213122523.12764-5-shikemeng@huaweicloud.com Signed-off-by: Kemeng Shi Cc: Mattew Wilcox Signed-off-by: Andrew Morton

Xarray: distinguish large entries correctly in xas_split_alloc()

2025-01-25T06:47:27Z

We don't support large entries which expand two more level xa_node in split. For case "xas->xa_shift + 2 * XA_CHUNK_SHIFT == order", we also need two level of xa_node to expand. Distinguish entry as large entry in case "xas->xa_shift + 2 * XA_CHUNK_SHIFT == order". As max order of folio in pagecache (MAX_PAGECACHE_ORDER) is <= (XA_CHUNK_SHIFT * 2 - 1), this change is more likely a cleanup... Link: https://lkml.kernel.org/r/20241213122523.12764-4-shikemeng@huaweicloud.com Signed-off-by: Kemeng Shi Cc: Mattew Wilcox Signed-off-by: Andrew Morton

Xarray: move forward index correctly in xas_pause()

2025-01-25T06:47:27Z

After xas_load(), xas->index could point to mid of found multi-index entry and xas->index's bits under node->shift maybe non-zero. The afterward xas_pause() will move forward xas->index with xa->node->shift with bits under node->shift un-masked and thus skip some index unexpectedly. Consider following case: Assume XA_CHUNK_SHIFT is 4. xa_store_range(xa, 16, 31, ...) xa_store(xa, 32, ...) XA_STATE(xas, xa, 17); xas_for_each(&xas,...) xas_load(&xas) /* xas->index = 17, xas->xa_offset = 1, xas->xa_node->xa_shift = 4 */ xas_pause() /* xas->index = 33, xas->xa_offset = 2, xas->xa_node->xa_shift = 4 */ As we can see, index of 32 is skipped unexpectedly. Fix this by mask bit under node->xa_shift when move forward index in xas_pause(). For now, this will not cause serious problems. Only minor problem like cachestat return less number of page status could happen. Link: https://lkml.kernel.org/r/20241213122523.12764-3-shikemeng@huaweicloud.com Signed-off-by: Kemeng Shi Cc: Mattew Wilcox Signed-off-by: Andrew Morton

Xarray: do not return sibling entries from xas_find_marked()

2025-01-25T06:47:27Z

Patch series "Fixes and cleanups to xarray", v5. This series contains some random fixes and cleanups to xarray. Patch 1-2 are fixes and patch 3-6 are cleanups. More details can be found in respective patches. This patch (of 5): Similar to issue fixed in commit cbc02854331ed ("XArray: Do not return sibling entries from xa_load()"), we may return sibling entries from xas_find_marked as following: Thread A: Thread B: xa_store_range(xa, entry, 6, 7, gfp); xa_set_mark(xa, 6, mark) XA_STATE(xas, xa, 6); xas_find_marked(&xas, 7, mark); offset = xas_find_chunk(xas, advance, mark); [offset is 6 which points to a valid entry] xa_store_range(xa, entry, 4, 7, gfp); entry = xa_entry(xa, node, 6); [entry is a sibling of 4] if (!xa_is_node(entry)) return entry; Skip sibling entry like xas_find() does to protect caller from seeing sibling entry from xas_find_marked() or caller may use sibling entry as a valid entry and crash the kernel. Besides, load_race() test is modified to catch mentioned issue and modified load_race() only passes after this fix is merged. Here is an example how this bug could be triggerred in tmpfs which enables large folio in mapping: Let's take a look at involved racer: 1. How pages could be created and dirtied in shmem file. write ksys_write vfs_write new_sync_write shmem_file_write_iter generic_perform_write shmem_write_begin shmem_get_folio shmem_allowable_huge_orders shmem_alloc_and_add_folios shmem_alloc_folio __folio_set_locked shmem_add_to_page_cache XA_STATE_ORDER(..., index, order) xax_store() shmem_write_end folio_mark_dirty() 2. How dirty pages could be deleted in shmem file. ioctl do_vfs_ioctl file_ioctl ioctl_preallocate vfs_fallocate shmem_fallocate shmem_truncate_range shmem_undo_range truncate_inode_folio filemap_remove_folio page_cache_delete xas_store(&xas, NULL); 3. How dirty pages could be lockless searched sync_file_range ksys_sync_file_range __filemap_fdatawrite_range filemap_fdatawrite_wbc do_writepages writeback_use_writepage writeback_iter writeback_get_folio filemap_get_folios_tag find_get_entry folio = xas_find_marked() folio_try_get(folio) Kernel will crash as following: 1.Create 2.Search 3.Delete /* write page 2,3 */ write ... shmem_write_begin XA_STATE_ORDER(xas, i_pages, index = 2, order = 1) xa_store(&xas, folio) shmem_write_end folio_mark_dirty() /* sync page 2 and page 3 */ sync_file_range ... find_get_entry folio = xas_find_marked() /* offset will be 2 */ offset = xas_find_chunk() /* delete page 2 and page 3 */ ioctl ... xas_store(&xas, NULL); /* write page 0-3 */ write ... shmem_write_begin XA_STATE_ORDER(xas, i_pages, index = 0, order = 2) xa_store(&xas, folio) shmem_write_end folio_mark_dirty(folio) /* get sibling entry from offset 2 */ entry = xa_entry(.., 2) /* use sibling entry as folio and crash kernel */ folio_try_get(folio) Link: https://lkml.kernel.org/r/20241213122523.12764-1-shikemeng@huaweicloud.com Link: https://lkml.kernel.org/r/20241213122523.12764-2-shikemeng@huaweicloud.com Signed-off-by: Kemeng Shi Cc: Mattew Wilcox [English fixes] Signed-off-by: Andrew Morton

xarray: extract helper from __xa_{insert,cmpxchg}

2025-01-13T04:20:58Z

Reduce code duplication by extracting a static inline function. This function is identical to __xa_cmpxchg with the exception that it does not coerce zero entries to null on the return path. [tamird@gmail.com: fix __xa_erase()] Link: https://lkml.kernel.org/r/CAJ-ks9kN_qddZ3Ne5d=cADu5POC1rHd4rQcbVSD_spnZOrLLZg@mail.gmail.com Link: https://lkml.kernel.org/r/20241112-xarray-insert-cmpxchg-v1-2-dc2bdd8c4136@gmail.com Signed-off-by: Tamir Duberstein Cc: Alice Ryhl Cc: Andreas Hindborg Cc: Matthew Wilcox Signed-off-by: Andrew Morton

xarray: extract xa_zero_to_null

2025-01-13T04:20:58Z

Patch series "xarray: extract __xa_cmpxchg_raw". This series reduces duplication between __xa_cmpxchg and __xa_insert by extracting a new function that does not coerce zero entries to null on the return path. The new function may be used by the upcoming Rust xarray abstraction in its reservation API where it is useful to tell the difference between zero entries and null slots. This patch (of 2): Reduce code duplication by extracting a static inline function that returns its argument if it is non-zero and NULL otherwise. This changes xas_result to check for errors before checking for zero but this cannot change the behavior of existing callers: - __xa_erase: passes the result of xas_store(_, NULL) which cannot fail. - __xa_store: passes the result of xas_store(_, entry) which may fail. xas_store calls xas_create when entry is not NULL which returns NULL on error, which is immediately checked. This should not change observable behavior. - __xa_cmpxchg: passes the result of xas_load(_) which might be zero. This would previously return NULL regardless of the outcome of xas_store but xas_store cannot fail if xas_load returns zero because there is no need to allocate memory. - xa_store_range: same as __xa_erase. Link: https://lkml.kernel.org/r/20241112-xarray-insert-cmpxchg-v1-0-dc2bdd8c4136@gmail.com Link: https://lkml.kernel.org/r/20241112-xarray-insert-cmpxchg-v1-1-dc2bdd8c4136@gmail.com Signed-off-by: Tamir Duberstein Cc: Alice Ryhl Cc: Andreas Hindborg Cc: Matthew Wilcox Signed-off-by: Andrew Morton

Merge tag 'mm-stable-2024-05-17-19-19' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

2024-05-19T16:21:03Z

Pull mm updates from Andrew Morton: "The usual shower of singleton fixes and minor series all over MM, documented (hopefully adequately) in the respective changelogs. Notable series include: - Lucas Stach has provided some page-mapping cleanup/consolidation/ maintainability work in the series "mm/treewide: Remove pXd_huge() API". - In the series "Allow migrate on protnone reference with MPOL_PREFERRED_MANY policy", Donet Tom has optimized mempolicy's MPOL_PREFERRED_MANY mode, yielding almost doubled performance in one test. - In their series "Memory allocation profiling" Kent Overstreet and Suren Baghdasaryan have contributed a means of determining (via /proc/allocinfo) whereabouts in the kernel memory is being allocated: number of calls and amount of memory. - Matthew Wilcox has provided the series "Various significant MM patches" which does a number of rather unrelated things, but in largely similar code sites. - In his series "mm: page_alloc: freelist migratetype hygiene" Johannes Weiner has fixed the page allocator's handling of migratetype requests, with resulting improvements in compaction efficiency. - In the series "make the hugetlb migration strategy consistent" Baolin Wang has fixed a hugetlb migration issue, which should improve hugetlb allocation reliability. - Liu Shixin has hit an I/O meltdown caused by readahead in a memory-tight memcg. Addressed in the series "Fix I/O high when memory almost met memcg limit". - In the series "mm/filemap: optimize folio adding and splitting" Kairui Song has optimized pagecache insertion, yielding ~10% performance improvement in one test. - Baoquan He has cleaned up and consolidated the early zone initialization code in the series "mm/mm_init.c: refactor free_area_init_core()". - Baoquan has also redone some MM initializatio code in the series "mm/init: minor clean up and improvement". - MM helper cleanups from Christoph Hellwig in his series "remove follow_pfn". - More cleanups from Matthew Wilcox in the series "Various page->flags cleanups". - Vlastimil Babka has contributed maintainability improvements in the series "memcg_kmem hooks refactoring". - More folio conversions and cleanups in Matthew Wilcox's series: "Convert huge_zero_page to huge_zero_folio" "khugepaged folio conversions" "Remove page_idle and page_young wrappers" "Use folio APIs in procfs" "Clean up __folio_put()" "Some cleanups for memory-failure" "Remove page_mapping()" "More folio compat code removal" - David Hildenbrand chipped in with "fs/proc/task_mmu: convert hugetlb functions to work on folis". - Code consolidation and cleanup work related to GUP's handling of hugetlbs in Peter Xu's series "mm/gup: Unify hugetlb, part 2". - Rick Edgecombe has developed some fixes to stack guard gaps in the series "Cover a guard gap corner case". - Jinjiang Tu has fixed KSM's behaviour after a fork+exec in the series "mm/ksm: fix ksm exec support for prctl". - Baolin Wang has implemented NUMA balancing for multi-size THPs. This is a simple first-cut implementation for now. The series is "support multi-size THP numa balancing". - Cleanups to vma handling helper functions from Matthew Wilcox in the series "Unify vma_address and vma_pgoff_address". - Some selftests maintenance work from Dev Jain in the series "selftests/mm: mremap_test: Optimizations and style fixes". - Improvements to the swapping of multi-size THPs from Ryan Roberts in the series "Swap-out mTHP without splitting". - Kefeng Wang has significantly optimized the handling of arm64's permission page faults in the series "arch/mm/fault: accelerate pagefault when badaccess" "mm: remove arch's private VM_FAULT_BADMAP/BADACCESS" - GUP cleanups from David Hildenbrand in "mm/gup: consistently call it GUP-fast". - hugetlb fault code cleanups from Vishal Moola in "Hugetlb fault path to use struct vm_fault". - selftests build fixes from John Hubbard in the series "Fix selftests/mm build without requiring "make headers"". - Memory tiering fixes/improvements from Ho-Ren (Jack) Chuang in the series "Improved Memory Tier Creation for CPUless NUMA Nodes". Fixes the initialization code so that migration between different memory types works as intended. - David Hildenbrand has improved follow_pte() and fixed an errant driver in the series "mm: follow_pte() improvements and acrn follow_pte() fixes". - David also did some cleanup work on large folio mapcounts in his series "mm: mapcount for large folios + page_mapcount() cleanups". - Folio conversions in KSM in Alex Shi's series "transfer page to folio in KSM". - Barry Song has added some sysfs stats for monitoring multi-size THP's in the series "mm: add per-order mTHP alloc and swpout counters". - Some zswap cleanups from Yosry Ahmed in the series "zswap same-filled and limit checking cleanups". - Matthew Wilcox has been looking at buffer_head code and found the documentation to be lacking. The series is "Improve buffer head documentation". - Multi-size THPs get more work, this time from Lance Yang. His series "mm/madvise: enhance lazyfreeing with mTHP in madvise_free" optimizes the freeing of these things. - Kemeng Shi has added more userspace-visible writeback instrumentation in the series "Improve visibility of writeback". - Kemeng Shi then sent some maintenance work on top in the series "Fix and cleanups to page-writeback". - Matthew Wilcox reduces mmap_lock traffic in the anon vma code in the series "Improve anon_vma scalability for anon VMAs". Intel's test bot reported an improbable 3x improvement in one test. - SeongJae Park adds some DAMON feature work in the series "mm/damon: add a DAMOS filter type for page granularity access recheck" "selftests/damon: add DAMOS quota goal test" - Also some maintenance work in the series "mm/damon/paddr: simplify page level access re-check for pageout" "mm/damon: misc fixes and improvements" - David Hildenbrand has disabled some known-to-fail selftests ni the series "selftests: mm: cow: flag vmsplice() hugetlb tests as XFAIL". - memcg metadata storage optimizations from Shakeel Butt in "memcg: reduce memory consumption by memcg stats". - DAX fixes and maintenance work from Vishal Verma in the series "dax/bus.c: Fixups for dax-bus locking"" * tag 'mm-stable-2024-05-17-19-19' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm: (426 commits) memcg, oom: cleanup unused memcg_oom_gfp_mask and memcg_oom_order selftests/mm: hugetlb_madv_vs_map: avoid test skipping by querying hugepage size at runtime mm/hugetlb: add missing VM_FAULT_SET_HINDEX in hugetlb_wp mm/hugetlb: add missing VM_FAULT_SET_HINDEX in hugetlb_fault selftests: cgroup: add tests to verify the zswap writeback path mm: memcg: make alloc_mem_cgroup_per_node_info() return bool mm/damon/core: fix return value from damos_wmark_metric_value mm: do not update memcg stats for NR_{FILE/SHMEM}_PMDMAPPED selftests: cgroup: remove redundant enabling of memory controller Docs/mm/damon/maintainer-profile: allow posting patches based on damon/next tree Docs/mm/damon/maintainer-profile: change the maintainer's timezone from PST to PT Docs/mm/damon/design: use a list for supported filters Docs/admin-guide/mm/damon/usage: fix wrong schemes effective quota update command Docs/admin-guide/mm/damon/usage: fix wrong example of DAMOS filter matching sysfs file selftests/damon: classify tests for functionalities and regressions selftests/damon/_damon_sysfs: use 'is' instead of '==' for 'None' selftests/damon/_damon_sysfs: find sysfs mount point from /proc/mounts selftests/damon/_damon_sysfs: check errors from nr_schemes file reads mm/damon/core: initialize ->esz_bp from damos_quota_init_priv() selftests/damon: add a test for DAMOS quota goal ...