Re: [PATCH 1/4] slab: do ClearSlabPfmemalloc() for all pages of slab

This churns code a lot more than is necessary. How about this as a
replacement patch?

---8<---
From: Joonsoo Kim <redacted>
Subject: [PATCH] slab: do ClearSlabPfmemalloc() for all pages of slab

Right now, we call ClearSlabPfmemalloc() for first page of slab when we
clear SlabPfmemalloc flag. This is fine for most swap-over-network use
cases as it is expected that order-0 pages are in use. Unfortunately it
is possible that that __ac_put_obj() checks SlabPfmemalloc on a tail page
and while this is harmless, it is sloppy. This patch ensures that the head
page is always used.

[mgorman@suse.de: Easier implementation, changelog cleanup]
Signed-off-by: Joonsoo Kim <redacted>
Signed-off-by: Mel Gorman <mgorman@suse.de>
---
 mm/slab.c |   12 +++++-------
 1 file changed, 5 insertions(+), 7 deletions(-)

diff --git a/mm/slab.c b/mm/slab.c
index 811af03..590d52a 100644
--- a/mm/slab.c
+++ b/mm/slab.c

@@ -1032,7 +1032,7 @@ static void *__ac_put_obj(struct kmem_cache *cachep, struct array_cache *ac,
 {
        if (unlikely(pfmemalloc_active)) {
                /* Some pfmemalloc slabs exist, check if this is one */
-               struct page *page = virt_to_page(objp);
+               struct page *page = virt_to_head_page(objp);
                if (PageSlabPfmemalloc(page))
                        set_obj_pfmemalloc(&objp);
        }

@@ -1919,12 +1919,10 @@ static void *kmem_getpages(struct kmem_cache *cachep, gfp_t flags, int nodeid)
        else
                add_zone_page_state(page_zone(page),
                        NR_SLAB_UNRECLAIMABLE, nr_pages);
-       for (i = 0; i < nr_pages; i++) {
+       for (i = 0; i < nr_pages; i++)
                __SetPageSlab(page + i);
-
-               if (page->pfmemalloc)
-                       SetPageSlabPfmemalloc(page + i);
-       }
+       if (page->pfmemalloc)
+               SetPageSlabPfmemalloc(page);

        if (kmemcheck_enabled && !(cachep->flags & SLAB_NOTRACK)) {
                kmemcheck_alloc_shadow(page, cachep->gfporder, flags, nodeid);

@@ -1955,9 +1953,9 @@ static void kmem_freepages(struct kmem_cache *cachep, void *addr)
        else
                sub_zone_page_state(page_zone(page),
                                NR_SLAB_UNRECLAIMABLE, nr_freed);
+       __ClearPageSlabPfmemalloc(page);
        while (i--) {
                BUG_ON(!PageSlab(page));
-               __ClearPageSlabPfmemalloc(page);
                __ClearPageSlab(page);
                page++;
        }