On Wed 16-07-14 12:28:00, Johannes Weiner wrote:
> Naoya-san reports that hugetlb pages now get charged as file cache,
> which wreaks all kinds of havoc during migration, uncharge etc.
>
> The file-specific charge path used to filter PageCompound(), but it
> wasn't commented and so it got lost when unifying the charge paths.
>
> We can't add PageCompound() back into a unified charge path because of
> THP, so filter huge pages directly in add_to_page_cache().
This looks a bit fragile to me but I understand your motivation to not
punish all the code paths with PageHuge check.
> Reported-by: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
> Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxx>
> ---
> mm/filemap.c | 20 ++++++++++++++------
> 1 file changed, 14 insertions(+), 6 deletions(-)
>
> diff --git a/mm/filemap.c b/mm/filemap.c
> index 114cd89c1cc2..c088ac01e856 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -31,6 +31,7 @@
> #include <linux/security.h>
> #include <linux/cpuset.h>
> #include <linux/hardirq.h> /* for BUG_ON(!in_atomic()) only */
> +#include <linux/hugetlb.h>
> #include <linux/memcontrol.h>
> #include <linux/cleancache.h>
> #include <linux/rmap.h>
> @@ -560,19 +561,24 @@ static int __add_to_page_cache_locked(struct page *page,
> pgoff_t offset, gfp_t gfp_mask,
> void **shadowp)
> {
> + int huge = PageHuge(page);
> struct mem_cgroup *memcg;
> int error;
>
> VM_BUG_ON_PAGE(!PageLocked(page), page);
> VM_BUG_ON_PAGE(PageSwapBacked(page), page);
>
> - error = mem_cgroup_try_charge(page, current->mm, gfp_mask, &memcg);
> - if (error)
> - return error;
> + if (!huge) {
> + error = mem_cgroup_try_charge(page, current->mm,
> + gfp_mask, &memcg);
> + if (error)
> + return error;
> + }
>
> error = radix_tree_maybe_preload(gfp_mask & ~__GFP_HIGHMEM);
> if (error) {
> - mem_cgroup_cancel_charge(page, memcg);
> + if (!huge)
> + mem_cgroup_cancel_charge(page, memcg);
> return error;
> }
>
> @@ -587,14 +593,16 @@ static int __add_to_page_cache_locked(struct page *page,
> goto err_insert;
> __inc_zone_page_state(page, NR_FILE_PAGES);
> spin_unlock_irq(&mapping->tree_lock);
> - mem_cgroup_commit_charge(page, memcg, false);
> + if (!huge)
> + mem_cgroup_commit_charge(page, memcg, false);
> trace_mm_filemap_add_to_page_cache(page);
> return 0;
> err_insert:
> page->mapping = NULL;
> /* Leave page->index set: truncation relies upon it */
> spin_unlock_irq(&mapping->tree_lock);
> - mem_cgroup_cancel_charge(page, memcg);
> + if (!huge)
> + mem_cgroup_cancel_charge(page, memcg);
> page_cache_release(page);
> return error;
> }
> --
> 2.0.0
>
--
Michal Hocko
SUSE Labs
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