On Fri, 2 Jun 2023 15:57:46 -0700 Mike Kravetz mike.kravetz@oracle.com wrote:
In commits d0ce0e47b323 and 91a2fb956ad99, hugetlb code was changed to use page_cache_next_miss to determine if a page was present in the page cache. However, the current implementation of page_cache_next_miss will always return the passed index if max_scan is 1 as in the hugetlb code. As a result, hugetlb code will always thing a page is present in the cache, even if that is not the case.
The patch which follows addresses the issue by changing the implementation of page_cache_next_miss and for consistency page_cache_prev_miss. Since such a patch also impacts the readahead code, I would suggest using the patch by Sidhartha Kumar [1] to fix the issue in 6.3 and this patch moving forward.
Well this is tricky.
This patch applies cleanly to 6.3, so if we add cc:stable to this patch, it will get backported, against your suggestion.
Sidhartha's patch [1] (which you recommend for -stable) is quite different from this patch. And Sidhartha's patch has no route to being tested in linux-next nor to being merged by Linus.
So problems. The preferable approach is to just backport this patch into -stable in the usual fashion. What are the risks in doing this?
If we would rather not modify page_cache_next/prev_miss, then a new interface as suggested by Ackerley Tng [2] could also be used.
Comments on the best way to fix moving forward would be appreciated.
[1] https://lore.kernel.org/linux-mm/20230505185301.534259-1-sidhartha.kumar@ora... [2] https://lore.kernel.org/linux-mm/98624c2f481966492b4eb8272aef747790229b73.16...
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(-)