linux-ext4 - Re: [PATCH 5/7] shmem: open code the page cache lookup in shmem_get_folio

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Date:   Sun, 19 Mar 2023 22:23:36 -0700 (PDT)
From:   Hugh Dickins <hughd@...gle.com>
To:     Christoph Hellwig <hch@....de>
cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Matthew Wilcox <willy@...radead.org>,
        Hugh Dickins <hughd@...gle.com>, linux-afs@...ts.infradead.org,
        linux-btrfs@...r.kernel.org, linux-ext4@...r.kernel.org,
        cluster-devel@...hat.com, linux-mm@...ck.org,
        linux-xfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-nilfs@...r.kernel.org
Subject: Re: [PATCH 5/7] shmem: open code the page cache lookup in
 shmem_get_folio_gfp

On Tue, 7 Mar 2023, Christoph Hellwig wrote:

> 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.
> 
> Signed-off-by: Christoph Hellwig <hch@....de>

Acked-by: Hugh Dickins <hughd@...gle.com>

but Andrew, please fold in this small improvement to its comment:

[PATCH] shmem: open code the page cache lookup in shmem_get_folio_gfp fix

Adjust the new comment line: shmem folio may have been swapped out.

Signed-off-by: Hugh Dickins <hughd@...gle.com>
---

 mm/shmem.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1905,7 +1905,7 @@ static int shmem_get_folio_gfp(struct inode *inode, pgoff_t index,
 	if (folio) {
 		folio_lock(folio);
 
-		/* Has the page been truncated? */
+		/* Has the folio been truncated or swapped out? */
 		if (unlikely(folio->mapping != mapping)) {
 			folio_unlock(folio);
 			folio_put(folio);