| Message ID | 20241113094727.1497722-4-mcgrof@kernel.org (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | enable bs > ps for block devices | expand |
On Wed, Nov 13, 2024 at 01:47:22AM -0800, Luis Chamberlain wrote: > +++ b/fs/buffer.c > @@ -2366,7 +2366,7 @@ int block_read_full_folio(struct folio *folio, get_block_t *get_block) > { > struct inode *inode = folio->mapping->host; > sector_t iblock, lblock; > - struct buffer_head *bh, *head, *arr[MAX_BUF_PER_PAGE]; > + struct buffer_head *bh, *head, *restart_bh = NULL, *arr[MAX_BUF_PER_PAGE]; MAX_BUF_PER_PAGE is a pain. There are configs like hexagon which have 256kB pages and so this array ends up being 512 * 8 bytes = 4kB in size which spews stack growth warnings. Can we just make this 8? > @@ -2385,6 +2385,7 @@ int block_read_full_folio(struct folio *folio, get_block_t *get_block) > iblock = div_u64(folio_pos(folio), blocksize); > lblock = div_u64(limit + blocksize - 1, blocksize); > bh = head; > +restart: > nr = 0; > i = 0; > > @@ -2417,7 +2418,12 @@ int block_read_full_folio(struct folio *folio, get_block_t *get_block) > continue; > } > arr[nr++] = bh; > - } while (i++, iblock++, (bh = bh->b_this_page) != head); > + } while (i++, iblock++, (bh = bh->b_this_page) != head && nr < MAX_BUF_PER_PAGE); > + > + if (nr == MAX_BUF_PER_PAGE && bh != head) > + restart_bh = bh; > + else > + restart_bh = NULL; > > if (fully_mapped) > folio_set_mappedtodisk(folio); > @@ -2450,6 +2456,15 @@ int block_read_full_folio(struct folio *folio, get_block_t *get_block) > else > submit_bh(REQ_OP_READ, bh); > } > + > + /* > + * Found more buffers than 'arr' could hold, > + * restart to submit the remaining ones. > + */ > + if (restart_bh) { > + bh = restart_bh; > + goto restart; > + } > return 0; This isn't right. Let's assume we need 16 blocks to fill in this folio and we have 8 entries in 'arr'. nr = 0; i = 0; do { if (buffer_uptodate(bh)) continue; ... arr[nr++] = bh; } while (i++, iblock++, (bh = bh->b_this_page) != head); for (i = 0; i < nr; i++) { bh = arr[i]; submit_bh(REQ_OP_READ, bh); OK, so first time round, we've submitted 8 I/Os. Now we see that restart_bh is not NULL and so we go round again. This time, we happen to find that the last 8 BHs are uptodate. And so we take this path: if (!nr) { /* * All buffers are uptodate or get_block() returned an * error when trying to map them - we can finish the read. */ folio_end_read(folio, !page_error); oops, we forgot about the 8 buffers we already submitted for read.
diff --git a/fs/buffer.c b/fs/buffer.c index 1fc9a50def0b..818c9c5840fe 100644 --- a/fs/buffer.c +++ b/fs/buffer.c @@ -2366,7 +2366,7 @@ int block_read_full_folio(struct folio *folio, get_block_t *get_block) { struct inode *inode = folio->mapping->host; sector_t iblock, lblock; - struct buffer_head *bh, *head, *arr[MAX_BUF_PER_PAGE]; + struct buffer_head *bh, *head, *restart_bh = NULL, *arr[MAX_BUF_PER_PAGE]; size_t blocksize; int nr, i; int fully_mapped = 1; @@ -2385,6 +2385,7 @@ int block_read_full_folio(struct folio *folio, get_block_t *get_block) iblock = div_u64(folio_pos(folio), blocksize); lblock = div_u64(limit + blocksize - 1, blocksize); bh = head; +restart: nr = 0; i = 0; @@ -2417,7 +2418,12 @@ int block_read_full_folio(struct folio *folio, get_block_t *get_block) continue; } arr[nr++] = bh; - } while (i++, iblock++, (bh = bh->b_this_page) != head); + } while (i++, iblock++, (bh = bh->b_this_page) != head && nr < MAX_BUF_PER_PAGE); + + if (nr == MAX_BUF_PER_PAGE && bh != head) + restart_bh = bh; + else + restart_bh = NULL; if (fully_mapped) folio_set_mappedtodisk(folio); @@ -2450,6 +2456,15 @@ int block_read_full_folio(struct folio *folio, get_block_t *get_block) else submit_bh(REQ_OP_READ, bh); } + + /* + * Found more buffers than 'arr' could hold, + * restart to submit the remaining ones. + */ + if (restart_bh) { + bh = restart_bh; + goto restart; + } return 0; } EXPORT_SYMBOL(block_read_full_folio);