+ shmem-open-code-the-page-cache-lookup-in-shmem_get_folio_gfp.patch added to mm-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: shmem: open code the page cache lookup in shmem_get_folio_gfp
has been added to the -mm mm-unstable branch.  Its filename is
     shmem-open-code-the-page-cache-lookup-in-shmem_get_folio_gfp.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/shmem-open-code-the-page-cache-lookup-in-shmem_get_folio_gfp.patch

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

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------------------------------------------------------
From: Christoph Hellwig <hch@lst.de>
Subject: shmem: open code the page cache lookup in shmem_get_folio_gfp
Date: Tue, 7 Mar 2023 15:34:08 +0100

Use the very low level filemap_get_entry helper to look up the entry in
the xarray, and then:

 - don't bother locking the folio if only doing a userfault notification
 - open code locking the page and checking for truncation in a related
   code block

This will allow to eventually remove the FGP_ENTRY flag.

Link: https://lkml.kernel.org/r/20230307143410.28031-6-hch@lst.de
Signed-off-by: Christoph Hellwig <hch@lst.de>
Cc: Andreas Gruenbacher <agruenba@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/shmem.c |   14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

--- a/mm/shmem.c~shmem-open-code-the-page-cache-lookup-in-shmem_get_folio_gfp
+++ a/mm/shmem.c
@@ -1859,12 +1859,10 @@ repeat:
 	sbinfo = SHMEM_SB(inode->i_sb);
 	charge_mm = vma ? vma->vm_mm : NULL;
 
-	folio = __filemap_get_folio(mapping, index, FGP_ENTRY | FGP_LOCK, 0);
+	folio = filemap_get_entry(mapping, index);
 	if (folio && vma && userfaultfd_minor(vma)) {
-		if (!xa_is_value(folio)) {
-			folio_unlock(folio);
+		if (!xa_is_value(folio))
 			folio_put(folio);
-		}
 		*fault_type = handle_userfault(vmf, VM_UFFD_MINOR);
 		return 0;
 	}
@@ -1880,6 +1878,14 @@ repeat:
 	}
 
 	if (folio) {
+		folio_lock(folio);
+
+		/* Has the page been truncated? */
+		if (unlikely(folio->mapping != mapping)) {
+			folio_unlock(folio);
+			folio_put(folio);
+			goto repeat;
+		}
 		if (sgp == SGP_WRITE)
 			folio_mark_accessed(folio);
 		if (folio_test_uptodate(folio))
_

Patches currently in -mm which might be from hch@lst.de are

ufs-dont-flush-page-immediately-for-dirsync-directories.patch
ocfs2-dont-use-write_one_page-in-ocfs2_duplicate_clusters_by_page.patch
mmjfs-move-write_one_page-folio_write_one-to-jfs.patch
mm-dont-look-at-xarray-value-entries-in-split_huge_pages_in_file.patch
mm-make-mapping_get_entry-available-outside-of-filemapc.patch
mm-use-filemap_get_entry-in-filemap_get_incore_folio.patch
shmem-remove-shmem_get_partial_folio.patch
shmem-open-code-the-page-cache-lookup-in-shmem_get_folio_gfp.patch
mm-remove-fgp_entry.patch
mm-return-an-err_ptr-from-__filemap_get_folio.patch