On Wed, Sep 8, 2021 at 12:58 PM David Howells <dhowells@xxxxxxxxxx> wrote:
>
> There's a loop in afs_extend_writeback() that adds extra pages to a write
> we want to make to improve the efficiency of the writeback by making it
> larger. This loop stops, however, if we hit a page we can't write back
> from immediately, but it doesn't get rid of the page ref we speculatively
> acquired.
>
> This was caused by the removal of the cleanup loop when the code switched
> from using find_get_pages_contig() to xarray scanning as the latter only
> gets a single page at a time, not a batch.
>
> Fix this by putting the page on a ref on an early break from the loop.
> Unfortunately, we can't just add that page to the pagevec we're employing
> as we'll go through that and add those pages to the RPC call.
>
> This was found by the generic/074 test. It leaks ~4GiB of RAM each time it
> is run - which can be observed with "top".
>
> Fixes: e87b03f5830e ("afs: Prepare for use of THPs")
> Reported-by: Marc Dionne <marc.dionne@xxxxxxxxxxxx>
> Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
> cc: linux-afs@xxxxxxxxxxxxxxxxxxx
> ---
>
> fs/afs/write.c | 10 ++++++++--
> 1 file changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/fs/afs/write.c b/fs/afs/write.c
> index c0534697268e..66b235266893 100644
> --- a/fs/afs/write.c
> +++ b/fs/afs/write.c
> @@ -471,13 +471,18 @@ static void afs_extend_writeback(struct address_space *mapping,
> }
>
> /* Has the page moved or been split? */
> - if (unlikely(page != xas_reload(&xas)))
> + if (unlikely(page != xas_reload(&xas))) {
> + put_page(page);
> break;
> + }
>
> - if (!trylock_page(page))
> + if (!trylock_page(page)) {
> + put_page(page);
> break;
> + }
> if (!PageDirty(page) || PageWriteback(page)) {
> unlock_page(page);
> + put_page(page);
> break;
> }
>
> @@ -487,6 +492,7 @@ static void afs_extend_writeback(struct address_space *mapping,
> t = afs_page_dirty_to(page, priv);
> if (f != 0 && !new_content) {
> unlock_page(page);
> + put_page(page);
> break;
> }
>
>
>
>
Reviewed-By: Marc Dionne <marc.dionne@xxxxxxxxxxxx>
Tested-By: Marc Dionne <marc.dionne@xxxxxxxxxxxx>
Marc
