linux-kernel - [PATCH 0/1] fix page_cache_next/prev

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Message-Id: <20230504233858.103068-1-mike.kravetz@oracle.com>
Date:   Thu,  4 May 2023 16:38:57 -0700
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-fsdevel@...r.kernel.org
Cc:     Matthew Wilcox <willy@...radead.org>,
        Ackerley Tng <ackerleytng@...gle.com>,
        Sidhartha Kumar <sidhartha.kumar@...cle.com>,
        Muchun Song <songmuchun@...edance.com>, vannapurve@...gle.com,
        erdemaktas@...gle.com, Andrew Morton <akpm@...ux-foundation.org>,
        Mike Kravetz <mike.kravetz@...cle.com>
Subject: [PATCH 0/1] fix page_cache_next/prev_miss off by one error

A cover letter is not necessary for this single patch as all information
is present in the commit message.  However, I am not 100% comfortable in
this change and would REALLY like to get comments from Matthew.

When reporting this issue, Ackerley Tng suggested a solution by creating
a new filemap_has_folio() function[1].  I believe that would be an
acceptable way to proceed although we would also need to change the
other use of page_cache_next_miss in hugetlb.c.

When looking more closely, it looks like page_cache_next/prev_miss do
not work exactly as described.  The result is the following patch.

IIUC, prior to hugetlb use of page_cache_next/prev_miss, it was only
used by readahead code.  My patch does change the return value and has
potential to impact the readahead users.  That is why I am not 100%
comfortable with this.

In any case, this is broken in v6.3 so we need a fix.

[1] https://lore.kernel.org/linux-mm/cover.1683069252.git.ackerleytng@google.com/
Mike Kravetz (1):
  page cache: fix page_cache_next/prev_miss off by one

 mm/filemap.c | 26 ++++++++++++++++----------
 1 file changed, 16 insertions(+), 10 deletions(-)

-- 
2.40.0