The patch titled
Subject: mm: memcg: lookup_page_cgroup (almost) never returns NULL
has been added to the -mm tree. Its filename is
mm-memcg-lookup_page_cgroup-almost-never-returns-null.patch
Before you just go and hit "reply", please:
a) Consider who else should be cc'ed
b) Prefer to cc a suitable mailing list as well
c) Ideally: find the original patch on the mailing list and do a
reply-to-all to that, adding suitable additional cc's
*** Remember to use Documentation/SubmitChecklist when testing your code ***
See http://userweb.kernel.org/~akpm/stuff/added-to-mm.txt to find
out what to do about this
The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/
------------------------------------------------------
From: Johannes Weiner <jweiner@xxxxxxxxxx>
Subject: mm: memcg: lookup_page_cgroup (almost) never returns NULL
Pages have their corresponding page_cgroup descriptors set up before they
are used in userspace, and thus managed by a memory cgroup.
The only time where lookup_page_cgroup() can return NULL is in the
CONFIG_DEBUG_VM-only page sanity checking code that executes while feeding
pages into the page allocator for the first time.
Remove the NULL checks against lookup_page_cgroup() results from all
callsites where we know that corresponding page_cgroup descriptors must be
allocated, and add a comment to the callsite that actually does have to
check the return value.
Signed-off-by: Johannes Weiner <jweiner@xxxxxxxxxx>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxx>
Cc: Balbir Singh <bsingharora@xxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/memcontrol.c | 11 +++++------
1 file changed, 5 insertions(+), 6 deletions(-)
diff -puN mm/memcontrol.c~mm-memcg-lookup_page_cgroup-almost-never-returns-null mm/memcontrol.c
--- a/mm/memcontrol.c~mm-memcg-lookup_page_cgroup-almost-never-returns-null
+++ a/mm/memcontrol.c
@@ -1894,9 +1894,6 @@ void mem_cgroup_update_page_stat(struct
bool need_unlock = false;
unsigned long uninitialized_var(flags);
- if (unlikely(!pc))
- return;
-
rcu_read_lock();
memcg = pc->mem_cgroup;
if (unlikely(!memcg || !PageCgroupUsed(pc)))
@@ -2669,8 +2666,6 @@ static int mem_cgroup_charge_common(stru
}
pc = lookup_page_cgroup(page);
- BUG_ON(!pc); /* XXX: remove this and move pc lookup into commit */
-
ret = __mem_cgroup_try_charge(mm, gfp_mask, nr_pages, &memcg, oom);
if (ret || !memcg)
return ret;
@@ -2942,7 +2937,7 @@ __mem_cgroup_uncharge_common(struct page
* Check if our page_cgroup is valid
*/
pc = lookup_page_cgroup(page);
- if (unlikely(!pc || !PageCgroupUsed(pc)))
+ if (unlikely(!PageCgroupUsed(pc)))
return NULL;
lock_page_cgroup(pc);
@@ -3326,6 +3321,10 @@ static struct page_cgroup *lookup_page_c
struct page_cgroup *pc;
pc = lookup_page_cgroup(page);
+ /*
+ * Can be NULL while feeding pages into the page allocator for
+ * the first time, i.e. during boot or memory hotplug.
+ */
if (likely(pc) && PageCgroupUsed(pc))
return pc;
return NULL;
_
Subject: Subject: mm: memcg: lookup_page_cgroup (almost) never returns NULL
Patches currently in -mm which might be from jweiner@xxxxxxxxxx are
mm-add-extra-free-kbytes-tunable.patch
mm-migrate-one-less-atomic-operation.patch
hugetlb-detect-race-upon-page-allocation-failure-during-cow.patch
hugetlb-clarify-hugetlb_instantiation_mutex-usage.patch
fadvise-only-initiate-writeback-for-specified-range-with-fadv_dontneed.patch
mm-exclude-reserved-pages-from-dirtyable-memory.patch
mm-exclude-reserved-pages-from-dirtyable-memory-fix.patch
mm-writeback-cleanups-in-preparation-for-per-zone-dirty-limits.patch
mm-try-to-distribute-dirty-pages-fairly-across-zones.patch
mm-filemap-pass-__gfp_write-from-grab_cache_page_write_begin.patch
btrfs-pass-__gfp_write-for-buffered-write-page-allocations.patch
mm-memcg-consolidate-hierarchy-iteration-primitives.patch
mm-vmscan-distinguish-global-reclaim-from-global-lru-scanning.patch
mm-vmscan-distinguish-between-memcg-triggering-reclaim-and-memcg-being-scanned.patch
mm-vmscan-distinguish-between-memcg-triggering-reclaim-and-memcg-being-scanned-checkpatch-fixes.patch
mm-memcg-per-priority-per-zone-hierarchy-scan-generations.patch
mm-move-memcg-hierarchy-reclaim-to-generic-reclaim-code.patch
mm-memcg-remove-optimization-of-keeping-the-root_mem_cgroup-lru-lists-empty.patch
mm-vmscan-convert-global-reclaim-to-per-memcg-lru-lists.patch
mm-collect-lru-list-heads-into-struct-lruvec.patch
mm-make-per-memcg-lru-lists-exclusive.patch
mm-memcg-remove-unused-node-section-info-from-pc-flags.patch
mm-memcg-remove-unused-node-section-info-from-pc-flags-fix.patch
mm-memcg-shorten-preempt-disabled-section-around-event-checks.patch
mm-oom_kill-remove-memcg-argument-from-oom_kill_task.patch
mm-unify-remaining-mem_cont-mem-etc-variable-names-to-memcg.patch
mm-memcg-clean-up-fault-accounting.patch
mm-memcg-lookup_page_cgroup-almost-never-returns-null.patch
mm-memcg-remove-unneeded-checks-from-newpage_charge.patch
mm-memcg-remove-unneeded-checks-from-uncharge_page.patch
thp-improve-the-error-code-path.patch
thp-remove-unnecessary-tlb-flush-for-mprotect.patch
thp-add-tlb_remove_pmd_tlb_entry.patch
thp-improve-order-in-lru-list-for-split-huge-page.patch
--
To unsubscribe from this list: send the line "unsubscribe mm-commits" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
