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SubjectRe: [PATCH] hugetlbfs: dirty pages as they are added to pagecache
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On Tue, 2018-10-23 at 10:30 -0700, Mike Kravetz wrote:
> ..... snip....
> Here is updated patch without the drop_caches change and updated
> fixes tag.
>
> From: Mike Kravetz <mike.kravetz@oracle.com>
>
> hugetlbfs: dirty pages as they are added to pagecache
>
> Some test systems were experiencing negative huge page reserve
> counts and incorrect file block counts. This was traced to
> /proc/sys/vm/drop_caches removing clean pages from hugetlbfs
> file pagecaches. When non-hugetlbfs explicit code removes the
> pages, the appropriate accounting is not performed.
>
> This can be recreated as follows:
> fallocate -l 2M /dev/hugepages/foo
> echo 1 > /proc/sys/vm/drop_caches
> fallocate -l 2M /dev/hugepages/foo
> grep -i huge /proc/meminfo
> AnonHugePages: 0 kB
> ShmemHugePages: 0 kB
> HugePages_Total: 2048
> HugePages_Free: 2047
> HugePages_Rsvd: 18446744073709551615
> HugePages_Surp: 0
> Hugepagesize: 2048 kB
> Hugetlb: 4194304 kB
> ls -lsh /dev/hugepages/foo
> 4.0M -rw-r--r--. 1 root root 2.0M Oct 17 20:05 /dev/hugepages/foo
>
> To address this issue, dirty pages as they are added to pagecache.
> This can easily be reproduced with fallocate as shown above. Read
> faulted pages will eventually end up being marked dirty. But there
> is a window where they are clean and could be impacted by code such
> as drop_caches. So, just dirty them all as they are added to the
> pagecache.
>
> Fixes: 6bda666a03f0 ("hugepages: fold find_or_alloc_pages into
> huge_no_page()")
> Cc: stable@vger.kernel.org
> Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
> ---
> mm/hugetlb.c | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 5c390f5a5207..7b5c0ad9a6bd 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -3690,6 +3690,12 @@ int huge_add_to_page_cache(struct page *page,
> struct address_space *mapping,
> return err;
> ClearPagePrivate(page);
>
> + /*
> + * set page dirty so that it will not be removed from
> cache/file
> + * by non-hugetlbfs specific code paths.
> + */
> + set_page_dirty(page);
> +
> spin_lock(&inode->i_lock);
> inode->i_blocks += blocks_per_huge_page(h);
> spin_unlock(&inode->i_lock);

This looks good.

Reviewed-by: Khalid Aziz <khalid.aziz@oracle.com>

--
Khalid

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