The patch titled Subject: mm/readahead: fix large folio support in async readahead has been added to the -mm mm-hotfixes-unstable branch. Its filename is mm-readahead-fix-large-folio-support-in-async-readahead.patch

This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...

This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------ From: Yafang Shao laoar.shao@gmail.com Subject: mm/readahead: fix large folio support in async readahead Date: Fri, 8 Nov 2024 22:17:10 +0800

When testing large folio support with XFS on our servers, we observed that only a few large folios are mapped when reading large files via mmap. After a thorough analysis, I identified it was caused by the `/sys/block/*/queue/read_ahead_kb` setting. On our test servers, this parameter is set to 128KB. After I tune it to 2MB, the large folio can work as expected. However, I believe the large folio behavior should not be dependent on the value of read_ahead_kb. It would be more robust if the kernel can automatically adopt to it.

With /sys/block/*/queue/read_ahead_kb set to 128KB and performing a sequential read on a 1GB file using MADV_HUGEPAGE, the differences in /proc/meminfo are as follows:

- before this patch FileHugePages: 18432 kB FilePmdMapped: 4096 kB

- after this patch FileHugePages: 1067008 kB FilePmdMapped: 1048576 kB

This shows that after applying the patch, the entire 1GB file is mapped to huge pages. The stable list is CCed, as without this patch, large folios don't function optimally in the readahead path.

It's worth noting that if read_ahead_kb is set to a larger value that isn't aligned with huge page sizes (e.g., 4MB + 128KB), it may still fail to map to hugepages.

Link: https://lkml.kernel.org/r/20241108141710.9721-1-laoar.shao@gmail.com Fixes: 4687fdbb805a ("mm/filemap: Support VM_HUGEPAGE for file mappings") Suggested-by: Matthew Wilcox willy@infradead.org Signed-off-by: Yafang Shao laoar.shao@gmail.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/readahead.c | 2 ++ 1 file changed, 2 insertions(+)

--- a/mm/readahead.c~mm-readahead-fix-large-folio-support-in-async-readahead +++ a/mm/readahead.c @@ -385,6 +385,8 @@ static unsigned long get_next_ra_size(st return 4 * cur; if (cur <= max / 2) return 2 * cur; + if (cur > max) + return cur; return max; }

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Patches currently in -mm which might be from laoar.shao@gmail.com are

mm-readahead-fix-large-folio-support-in-async-readahead.patch