[PATCH 2/2] btrfs: simplify heuristic_collect_sample() to handle large folios better
From: Qu Wenruo <hidden>
Date: 2026-09-10 02:06:25
Subsystem:
btrfs file system, filesystems (vfs and infrastructure), the rest · Maintainers:
David Sterba, Alexander Viro, Christian Brauner, Linus Torvalds
Currently heuristic_collect_sample() is purely page size based, and it has a lot of extra handling just inside the page. However we already have large folio support, there is no need to look up the same folio again and again. Simplify the handling by: - Use @cur as the iterator instead of page index - Handle the sample copying on a per-folio basis Although kmap_local_folio() requires an offset to handle HIGHMEM page mapping, we have rejected large folios for HIGHMEM systems completely. So we can safely handle all sample copying inside the folio in one go. - Remove unnecessary unaligned range handling All the range passed in should be block aligned, thus there is no need to handle cases where sample crosses the block boundary. Signed-off-by: Qu Wenruo <redacted> --- fs/btrfs/compression.c | 40 ++++++++++++++++------------------------ 1 file changed, 16 insertions(+), 24 deletions(-)
diff --git a/fs/btrfs/compression.c b/fs/btrfs/compression.c
index 0134b9253702..ad90e14032db 100644
--- a/fs/btrfs/compression.c
+++ b/fs/btrfs/compression.c@@ -1489,10 +1489,8 @@ static void heuristic_collect_sample(struct inode *inode, u64 start, u64 end, struct heuristic_ws *ws) { const u32 blocksize = BTRFS_I(inode)->root->fs_info->sectorsize; - struct folio *folio; - pgoff_t index, index_end; - u32 i, curr_sample_pos; - u8 *in_data; + u64 cur = start; + u32 curr_sample_pos = 0; ASSERT(IS_ALIGNED(start, blocksize) && IS_ALIGNED(end + 1, blocksize));
@@ -1508,33 +1506,27 @@ static void heuristic_collect_sample(struct inode *inode, u64 start, u64 end, if (end + 1 - start > BTRFS_MAX_UNCOMPRESSED) end = start + BTRFS_MAX_UNCOMPRESSED - 1; - index = start >> PAGE_SHIFT; - index_end = end >> PAGE_SHIFT; + while (cur < end) { + struct folio *folio; + void *in_data; + u64 next_pos; - curr_sample_pos = 0; - while (index <= index_end) { - folio = filemap_get_folio(inode->i_mapping, index); + folio = filemap_get_folio(inode->i_mapping, cur >> PAGE_SHIFT); + /* All folios inside the range should exist and be locked. */ ASSERT(!IS_ERR(folio)); - in_data = kmap_local_folio(folio, - offset_in_folio(folio, (u64)index << PAGE_SHIFT)); - /* Handle case where the start is not aligned to PAGE_SIZE */ - i = start % PAGE_SIZE; - while (i < PAGE_SIZE - SAMPLING_READ_SIZE) { - /* Don't sample any garbage from the last page */ - if (start > end + 1 - SAMPLING_READ_SIZE) - break; - memcpy(&ws->sample[curr_sample_pos], &in_data[i], - SAMPLING_READ_SIZE); - i += SAMPLING_INTERVAL; - start += SAMPLING_INTERVAL; + next_pos = min_t(u64, end + 1, folio_next_pos(folio)); + in_data = kmap_local_folio(folio, 0); + + for (; cur < next_pos; cur += SAMPLING_INTERVAL) { + memcpy(&ws->sample[curr_sample_pos], + in_data + offset_in_folio(folio, cur), + SAMPLING_READ_SIZE); curr_sample_pos += SAMPLING_READ_SIZE; } kunmap_local(in_data); folio_put(folio); - - index++; + cur = next_pos; } - ws->sample_size = curr_sample_pos; }
--
2.55.0