On Wed 06-11-19 06:02:31, Yang Shi wrote:
> The shmem_writepage() uses GFP_ATOMIC to allocate swap cache.
> GFP_ATOMIC used to mean __GFP_HIGH, but now it means __GFP_HIGH |
> __GFP_ATOMIC | __GFP_KSWAPD_RECLAIM. However, shmem_writepage() should
> write out to swap only in response to memory pressure, so
> __GFP_KSWAPD_RECLAIM looks useless since the caller may be kswapd itself
> or in direct reclaim already.
What kind of problem are you trying to fix here?
> In addition, XArray node allocations from PF_MEMALLOC contexts could
> completely exhaust the page allocator, __GFP_NOMEMALLOC stops emergency
> reserves from being allocated.
I am not really familiar with XArray much, could you be more specific
please?
> Here just copy the gfp flags used by add_to_swap().
>
> Cc: Hugh Dickins <hughd@xxxxxxxxxx>
> Signed-off-by: Yang Shi <yang.shi@xxxxxxxxxxxxxxxxx>
> ---
> mm/shmem.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/mm/shmem.c b/mm/shmem.c
> index 220be9f..9691dec 100644
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -1369,7 +1369,8 @@ static int shmem_writepage(struct page *page, struct writeback_control *wbc)
> if (list_empty(&info->swaplist))
> list_add(&info->swaplist, &shmem_swaplist);
>
> - if (add_to_swap_cache(page, swap, GFP_ATOMIC) == 0) {
> + if (add_to_swap_cache(page, swap,
> + __GFP_HIGH | __GFP_NOMEMALLOC | __GFP_NOWARN) == 0) {
> spin_lock_irq(&info->lock);
> shmem_recalc_inode(inode);
> info->swapped++;
> --
> 1.8.3.1
--
Michal Hocko
SUSE Labs
