Extent buffer pages allocated by alloc_extent_buffer() are attached to btree_inode->i_mapping (the buffer_tree path), reach the LRU, and are served by the btree_migrate_folio aops in fs/btrfs/disk-io.c. They are migratable in practice once their owning extent buffer hits refs == 1, which happens naturally as tree roots rotate. The buddy allocator classifies them by GFP, however, and bare GFP_NOFS lands them in MIGRATE_UNMOVABLE pageblocks. The result: every btree_inode page we read in pins an unmovable pageblock from the page-superblock allocator's perspective, even though the page itself can be moved. Add __GFP_MOVABLE to that one allocation site (alloc_extent_buffer's call to alloc_eb_folio_array). Plumb the flag through alloc_eb_folio_array → btrfs_alloc_page_array as a `gfp_t extra_gfp` parameter. All other call sites pass 0. Three categories of caller stay on bare GFP_NOFS, deliberately: - alloc_dummy_extent_buffer / btrfs_clone_extent_buffer: the resulting eb is EXTENT_BUFFER_UNMAPPED, folio->mapping stays NULL, the folios never enter LRU, never get migrate_folio aops. Tagging them __GFP_MOVABLE would violate the page allocator's migrability contract and they would defeat compaction in MOVABLE pageblocks where isolate_migratepages_block skips non-LRU non-movable_ops pages outright. - btrfs_alloc_page_array callers in fs/btrfs/raid56.c (stripe pages), fs/btrfs/inode.c (encoded reads), fs/btrfs/ioctl.c (uring encoded reads), fs/btrfs/relocation.c (relocation buffers): same contract violation. raid56 stripe_pages additionally persist in the stripe cache (RBIO_CACHE_SIZE=1024) well beyond a single I/O, so they are not transient enough to hand-wave the contract. - btrfs_alloc_folio_array caller in fs/btrfs/scrub.c (stripe folios): same -- stripe->folios[] are private buffers freed via folio_put in release_scrub_stripe. This change targets the dominant fragmentation source observed on the page-superblock series: ~28 GB of btree_inode pages parked across many tainted superpageblocks on a 250 GB test system with btrfs root, preventing 1 GiB hugepage allocation from those regions. With the movable hint, those pages now land in MOVABLE pageblocks where the existing background defragger drains them through the standard PB_has_movable gate, no LRU-sample fallback needed. Cc: Chris Mason Cc: David Sterba Cc: Boris Burkov Cc: linux-btrfs@vger.kernel.org Signed-off-by: Rik van Riel Assisted-by: Claude:claude-opus-4.7 syzkaller --- fs/btrfs/extent_io.c | 69 ++++++++++++++++++++++++++++++------------- fs/btrfs/extent_io.h | 4 +-- fs/btrfs/inode.c | 2 +- fs/btrfs/ioctl.c | 2 +- fs/btrfs/raid56.c | 6 ++-- fs/btrfs/relocation.c | 2 +- fs/btrfs/scrub.c | 3 +- 7 files changed, 59 insertions(+), 29 deletions(-) diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c index 2275189b7860..563c4a7eaa36 100644 --- a/fs/btrfs/extent_io.c +++ b/fs/btrfs/extent_io.c @@ -620,24 +620,33 @@ static void end_bbio_data_read(struct btrfs_bio *bbio) } /* - * Populate every free slot in a provided array with folios using GFP_NOFS. + * Populate every free slot in a provided array with folios using + * GFP_NOFS plus optional caller-supplied flags. * - * @nr_folios: number of folios to allocate - * @order: the order of the folios to be allocated - * @folio_array: the array to fill with folios; any existing non-NULL entries in - * the array will be skipped + * @nr_folios: number of folios to allocate + * @order: folio order + * @folio_array: array to fill with folios; non-NULL entries are skipped + * @extra_gfp: extra GFP flags OR'd into GFP_NOFS. The only value used + * today is __GFP_MOVABLE, which the extent-buffer real-mapping + * path (alloc_extent_buffer) passes when the resulting folios + * will be attached to btree_inode->i_mapping (added to LRU, + * served by the btree_migrate_folio aops). Pass 0 for + * everything else; folios allocated by other callers stay in + * driver-owned arrays, never reach LRU and never register + * movable_ops, so they cannot satisfy the __GFP_MOVABLE + * migrability contract. * * Return: 0 if all folios were able to be allocated; * -ENOMEM otherwise, the partially allocated folios would be freed and * the array slots zeroed */ int btrfs_alloc_folio_array(unsigned int nr_folios, unsigned int order, - struct folio **folio_array) + struct folio **folio_array, gfp_t extra_gfp) { for (int i = 0; i < nr_folios; i++) { if (folio_array[i]) continue; - folio_array[i] = folio_alloc(GFP_NOFS, order); + folio_array[i] = folio_alloc(GFP_NOFS | extra_gfp, order); if (!folio_array[i]) goto error; } @@ -652,21 +661,27 @@ int btrfs_alloc_folio_array(unsigned int nr_folios, unsigned int order, } /* - * Populate every free slot in a provided array with pages, using GFP_NOFS. + * Populate every free slot in a provided array with pages, using GFP_NOFS + * plus optional caller-supplied flags. * - * @nr_pages: number of pages to allocate - * @page_array: the array to fill with pages; any existing non-null entries in - * the array will be skipped - * @nofail: whether using __GFP_NOFAIL flag + * @nr_pages: number of pages to allocate + * @page_array: array to fill; non-NULL entries are skipped + * @nofail: whether to use __GFP_NOFAIL + * @extra_gfp: extra GFP flags OR'd into the base mask. The only value used + * today is __GFP_MOVABLE, which the extent-buffer real-mapping + * path passes when the resulting pages will be attached to + * btree_inode->i_mapping. See btrfs_alloc_folio_array() for + * the full migrability rationale. * * Return: 0 if all pages were able to be allocated; * -ENOMEM otherwise, the partially allocated pages would be freed and * the array slots zeroed */ int btrfs_alloc_page_array(unsigned int nr_pages, struct page **page_array, - bool nofail) + bool nofail, gfp_t extra_gfp) { - const gfp_t gfp = nofail ? (GFP_NOFS | __GFP_NOFAIL) : GFP_NOFS; + const gfp_t gfp = (nofail ? (GFP_NOFS | __GFP_NOFAIL) : GFP_NOFS) | + extra_gfp; unsigned int allocated; for (allocated = 0; allocated < nr_pages;) { @@ -689,14 +704,23 @@ int btrfs_alloc_page_array(unsigned int nr_pages, struct page **page_array, * Populate needed folios for the extent buffer. * * For now, the folios populated are always in order 0 (aka, single page). + * + * @movable: pass true only when the resulting pages will be attached to + * btree_inode->i_mapping (the alloc_extent_buffer real path). + * Cloned/dummy extent buffers (EXTENT_BUFFER_UNMAPPED) leave + * folio->mapping NULL, never enter the LRU, and never get the + * btree_migrate_folio aops, so __GFP_MOVABLE would violate the + * page-allocator's migrability contract for them. */ -static int alloc_eb_folio_array(struct extent_buffer *eb, bool nofail) +static int alloc_eb_folio_array(struct extent_buffer *eb, bool nofail, + bool movable) { struct page *page_array[INLINE_EXTENT_BUFFER_PAGES] = { 0 }; int num_pages = num_extent_pages(eb); int ret; - ret = btrfs_alloc_page_array(num_pages, page_array, nofail); + ret = btrfs_alloc_page_array(num_pages, page_array, nofail, + movable ? __GFP_MOVABLE : 0); if (ret < 0) return ret; @@ -3097,7 +3121,7 @@ struct extent_buffer *btrfs_clone_extent_buffer(const struct extent_buffer *src) */ set_bit(EXTENT_BUFFER_UNMAPPED, &new->bflags); - ret = alloc_eb_folio_array(new, false); + ret = alloc_eb_folio_array(new, false, false); if (ret) goto release_eb; @@ -3138,7 +3162,7 @@ struct extent_buffer *alloc_dummy_extent_buffer(struct btrfs_fs_info *fs_info, if (!eb) return NULL; - ret = alloc_eb_folio_array(eb, false); + ret = alloc_eb_folio_array(eb, false, false); if (ret) goto release_eb; @@ -3491,8 +3515,13 @@ struct extent_buffer *alloc_extent_buffer(struct btrfs_fs_info *fs_info, } reallocate: - /* Allocate all pages first. */ - ret = alloc_eb_folio_array(eb, true); + /* + * Allocate all pages first. These will be attached to + * btree_inode->i_mapping below (added to LRU, served by + * btree_migrate_folio), so request __GFP_MOVABLE so the + * page allocator places them in MOVABLE pageblocks. + */ + ret = alloc_eb_folio_array(eb, true, true); if (ret < 0) { btrfs_free_folio_state(prealloc); goto out; diff --git a/fs/btrfs/extent_io.h b/fs/btrfs/extent_io.h index b310a5145cf6..5e263f07b59d 100644 --- a/fs/btrfs/extent_io.h +++ b/fs/btrfs/extent_io.h @@ -387,9 +387,9 @@ void btrfs_clear_buffer_dirty(struct btrfs_trans_handle *trans, struct extent_buffer *buf); int btrfs_alloc_page_array(unsigned int nr_pages, struct page **page_array, - bool nofail); + bool nofail, gfp_t extra_gfp); int btrfs_alloc_folio_array(unsigned int nr_folios, unsigned int order, - struct folio **folio_array); + struct folio **folio_array, gfp_t extra_gfp); #ifdef CONFIG_BTRFS_FS_RUN_SANITY_TESTS bool find_lock_delalloc_range(struct inode *inode, diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c index 906d5c21ebc4..85f56ab815f9 100644 --- a/fs/btrfs/inode.c +++ b/fs/btrfs/inode.c @@ -9659,7 +9659,7 @@ ssize_t btrfs_encoded_read_regular(struct kiocb *iocb, struct iov_iter *iter, pages = kzalloc_objs(struct page *, nr_pages, GFP_NOFS); if (!pages) return -ENOMEM; - ret = btrfs_alloc_page_array(nr_pages, pages, false); + ret = btrfs_alloc_page_array(nr_pages, pages, false, 0); if (ret) { ret = -ENOMEM; goto out; diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c index a39460bf68a7..77091915cacc 100644 --- a/fs/btrfs/ioctl.c +++ b/fs/btrfs/ioctl.c @@ -4621,7 +4621,7 @@ static int btrfs_uring_read_extent(struct kiocb *iocb, struct iov_iter *iter, pages = kzalloc_objs(struct page *, nr_pages, GFP_NOFS); if (!pages) return -ENOMEM; - ret = btrfs_alloc_page_array(nr_pages, pages, 0); + ret = btrfs_alloc_page_array(nr_pages, pages, 0, 0); if (ret) { ret = -ENOMEM; goto out_fail; diff --git a/fs/btrfs/raid56.c b/fs/btrfs/raid56.c index 08ee8f316d96..4135bac62be1 100644 --- a/fs/btrfs/raid56.c +++ b/fs/btrfs/raid56.c @@ -1123,7 +1123,7 @@ static int alloc_rbio_pages(struct btrfs_raid_bio *rbio) { int ret; - ret = btrfs_alloc_page_array(rbio->nr_pages, rbio->stripe_pages, false); + ret = btrfs_alloc_page_array(rbio->nr_pages, rbio->stripe_pages, false, 0); if (ret < 0) return ret; /* Mapping all sectors */ @@ -1138,7 +1138,7 @@ static int alloc_rbio_parity_pages(struct btrfs_raid_bio *rbio) int ret; ret = btrfs_alloc_page_array(rbio->nr_pages - data_pages, - rbio->stripe_pages + data_pages, false); + rbio->stripe_pages + data_pages, false, 0); if (ret < 0) return ret; @@ -1732,7 +1732,7 @@ static int alloc_rbio_data_pages(struct btrfs_raid_bio *rbio) const int data_pages = rbio->nr_data * rbio->stripe_npages; int ret; - ret = btrfs_alloc_page_array(data_pages, rbio->stripe_pages, false); + ret = btrfs_alloc_page_array(data_pages, rbio->stripe_pages, false, 0); if (ret < 0) return ret; diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c index 3ebaf5880125..6f6d25724fb8 100644 --- a/fs/btrfs/relocation.c +++ b/fs/btrfs/relocation.c @@ -4038,7 +4038,7 @@ static int copy_remapped_data(struct btrfs_fs_info *fs_info, u64 old_addr, if (!pages) return -ENOMEM; - ret = btrfs_alloc_page_array(nr_pages, pages, 0); + ret = btrfs_alloc_page_array(nr_pages, pages, 0, 0); if (ret) { ret = -ENOMEM; goto end; diff --git a/fs/btrfs/scrub.c b/fs/btrfs/scrub.c index 1ac609239cbe..4089e80077cc 100644 --- a/fs/btrfs/scrub.c +++ b/fs/btrfs/scrub.c @@ -369,7 +369,8 @@ static int init_scrub_stripe(struct btrfs_fs_info *fs_info, ASSERT(BTRFS_STRIPE_LEN >> min_folio_shift <= SCRUB_STRIPE_MAX_FOLIOS); ret = btrfs_alloc_folio_array(BTRFS_STRIPE_LEN >> min_folio_shift, - fs_info->block_min_order, stripe->folios); + fs_info->block_min_order, stripe->folios, + 0); if (ret < 0) goto error; -- 2.54.0