From: Chi Zhiling Date: Mon, 28 Jul 2025 08:39:52 +0000 (+0800) Subject: mm/filemap: skip non-uptodate folio if there are available folios X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=3b6ebf430e837659859a9b0be817b8ddbe32177b;p=users%2Fjedix%2Flinux-maple.git mm/filemap: skip non-uptodate folio if there are available folios When reading data exceeding the maximum IO size, the operation is split into multiple IO requests, but the data isn't immediately copied to userspace after each IO completion. For example, when reading 2560k data from a device with 1280k maximum IO size, the following sequence occurs: 1. read 1280k 2. copy 41 pages and issue read ahead for next 1280k 3. copy 31 pages to user buffer 4. wait the next 1280k 5. copy 8 pages to user buffer 6. copy 20 folios(64k) to user buffer The 8 pages in step 5 are copied after the second 1280k completes(step 4) due to waiting for a non-uptodate folio in filemap_update_page. We can copy the 8 pages before the second 1280k completes(step 4) to reduce the latency of this read operation. After applying the patch, these 8 pages will be copied before the next IO completes: 1. read 1280k 2. copy 41 pages and issue read ahead for next 1280k 3. copy 31 pages to user buffer 4. copy 8 pages to user buffer 5. wait the next 1280k 6. copy 20 folios(64k) to user buffer This patch drops a setting of IOCB_NOWAIT for AIO, which is fine because filemap_read will set it again for AIO. The final solution provided by Matthew Wilcox: Link: https://lore.kernel.org/linux-fsdevel/aIDy076Sxt544qja@casper.infradead.org/ Link: https://lkml.kernel.org/r/20250728083952.75518-3-chizhiling@163.com Signed-off-by: Chi Zhiling Suggested-by: Matthew Wilcox (Oracle) Cc: Christoph Hellwig Cc: Jan Kara Signed-off-by: Andrew Morton --- diff --git a/mm/filemap.c b/mm/filemap.c index d6f95513241f0..6e954156bb77f 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -2622,9 +2622,10 @@ retry: goto err; } if (!folio_test_uptodate(folio)) { - if ((iocb->ki_flags & IOCB_WAITQ) && - folio_batch_count(fbatch) > 1) - iocb->ki_flags |= IOCB_NOWAIT; + if (folio_batch_count(fbatch) > 1) { + err = -EAGAIN; + goto err; + } err = filemap_update_page(iocb, mapping, count, folio, need_uptodate); if (err)