The patch titled Subject: fs: reduce stack usage in __mpage_writepage has been added to the -mm mm-unstable branch. Its filename is fs-reduce-stack-usage-in-__mpage_writepage.patch This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/fs-reduce-stack-usage-in-__mpage_writepage.patch This patch will later appear in the mm-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** The -mm tree is included into linux-next via the mm-everything branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm and is updated there every 2-3 working days ------------------------------------------------------ From: "Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx> Subject: fs: reduce stack usage in __mpage_writepage Date: Fri, 15 Dec 2023 20:02:34 +0000 Some architectures support a very large PAGE_SIZE, so instead of the 8 pointers we see with a 4kB PAGE_SIZE, we can see 128 pointers with 64kB or so many on Hexagon that it trips compiler warnings about exceeding stack frame size. All we're doing with this array is checking for block contiguity, which we can as well do by remembering the address of the first block in the page and checking this block is at the appropriate offset from that address. Link: https://lkml.kernel.org/r/20231215200245.748418-4-willy@xxxxxxxxxxxxx Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx> Reviewed-by: Christoph Hellwig <hch@xxxxxx> Reviewed-by: Jens Axboe <axboe@xxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- fs/mpage.c | 20 ++++++++++++-------- 1 file changed, 12 insertions(+), 8 deletions(-) --- a/fs/mpage.c~fs-reduce-stack-usage-in-__mpage_writepage +++ a/fs/mpage.c @@ -466,7 +466,7 @@ static int __mpage_writepage(struct foli const unsigned blocks_per_page = PAGE_SIZE >> blkbits; sector_t last_block; sector_t block_in_file; - sector_t blocks[MAX_BUF_PER_PAGE]; + sector_t first_block; unsigned page_block; unsigned first_unmapped = blocks_per_page; struct block_device *bdev = NULL; @@ -504,10 +504,12 @@ static int __mpage_writepage(struct foli if (!buffer_dirty(bh) || !buffer_uptodate(bh)) goto confused; if (page_block) { - if (bh->b_blocknr != blocks[page_block-1] + 1) + if (bh->b_blocknr != first_block + page_block) goto confused; + } else { + first_block = bh->b_blocknr; } - blocks[page_block++] = bh->b_blocknr; + page_block++; boundary = buffer_boundary(bh); if (boundary) { boundary_block = bh->b_blocknr; @@ -556,10 +558,12 @@ static int __mpage_writepage(struct foli boundary_bdev = map_bh.b_bdev; } if (page_block) { - if (map_bh.b_blocknr != blocks[page_block-1] + 1) + if (map_bh.b_blocknr != first_block + page_block) goto confused; + } else { + first_block = map_bh.b_blocknr; } - blocks[page_block++] = map_bh.b_blocknr; + page_block++; boundary = buffer_boundary(&map_bh); bdev = map_bh.b_bdev; if (block_in_file == last_block) @@ -591,7 +595,7 @@ page_is_mapped: /* * This page will go to BIO. Do we need to send this BIO off first? */ - if (bio && mpd->last_block_in_bio != blocks[0] - 1) + if (bio && mpd->last_block_in_bio != first_block - 1) bio = mpage_bio_submit_write(bio); alloc_new: @@ -599,7 +603,7 @@ alloc_new: bio = bio_alloc(bdev, BIO_MAX_VECS, REQ_OP_WRITE | wbc_to_write_flags(wbc), GFP_NOFS); - bio->bi_iter.bi_sector = blocks[0] << (blkbits - 9); + bio->bi_iter.bi_sector = first_block << (blkbits - 9); wbc_init_bio(wbc, bio); } @@ -627,7 +631,7 @@ alloc_new: boundary_block, 1 << blkbits); } } else { - mpd->last_block_in_bio = blocks[blocks_per_page - 1]; + mpd->last_block_in_bio = first_block + blocks_per_page - 1; } goto out; _ Patches currently in -mm which might be from willy@xxxxxxxxxxxxx are mm-memory-failure-pass-the-folio-and-the-page-to-collect_procs.patch mm-memory-failure-check-the-mapcount-of-the-precise-page.patch mm-memory-failure-cast-index-to-loff_t-before-shifting-it.patch mailmap-add-an-old-address-for-naoya-horiguchi.patch buffer-return-bool-from-grow_dev_folio.patch buffer-calculate-block-number-inside-folio_init_buffers.patch buffer-fix-grow_buffers-for-block-size-page_size.patch buffer-cast-block-to-loff_t-before-shifting-it.patch buffer-fix-various-functions-for-block-size-page_size.patch buffer-handle-large-folios-in-__block_write_begin_int.patch buffer-fix-more-functions-for-block-size-page_size.patch mm-convert-ksm_might_need_to_copy-to-work-on-folios.patch mm-convert-ksm_might_need_to_copy-to-work-on-folios-fix.patch mm-remove-pageanonexclusive-assertions-in-unuse_pte.patch mm-convert-unuse_pte-to-use-a-folio-throughout.patch mm-remove-some-calls-to-page_add_new_anon_rmap.patch mm-remove-stale-example-from-comment.patch mm-remove-references-to-page_add_new_anon_rmap-in-comments.patch mm-convert-migrate_vma_insert_page-to-use-a-folio.patch mm-convert-collapse_huge_page-to-use-a-folio.patch mm-remove-page_add_new_anon_rmap-and-lru_cache_add_inactive_or_unevictable.patch mm-return-the-folio-from-__read_swap_cache_async.patch mm-pass-a-folio-to-__swap_writepage.patch mm-pass-a-folio-to-swap_writepage_fs.patch mm-pass-a-folio-to-swap_writepage_bdev_sync.patch mm-pass-a-folio-to-swap_writepage_bdev_async.patch mm-pass-a-folio-to-swap_readpage_fs.patch mm-pass-a-folio-to-swap_readpage_bdev_sync.patch mm-pass-a-folio-to-swap_readpage_bdev_async.patch mm-convert-swap_page_sector-to-swap_folio_sector.patch mm-convert-swap_readpage-to-swap_read_folio.patch mm-remove-page_swap_info.patch mm-return-a-folio-from-read_swap_cache_async.patch mm-convert-swap_cluster_readahead-and-swap_vma_readahead-to-return-a-folio.patch fs-remove-clean_page_buffers.patch fs-convert-clean_buffers-to-take-a-folio.patch fs-reduce-stack-usage-in-__mpage_writepage.patch fs-reduce-stack-usage-in-do_mpage_readpage.patch adfs-remove-writepage-implementation.patch bfs-remove-writepage-implementation.patch hfs-really-remove-hfs_writepage.patch hfsplus-really-remove-hfsplus_writepage.patch minix-remove-writepage-implementation.patch ocfs2-remove-writepage-implementation.patch sysv-remove-writepage-implementation.patch ufs-remove-writepage-implementation.patch fs-convert-block_write_full_page-to-block_write_full_folio.patch fs-remove-the-bh_end_io-argument-from-__block_write_full_folio.patch