memcg, thp: do not invoke oom killer on thp charges

From: Michal Hocko <[email protected]>

David has noticed that THP memcg charge can trigger the oom killer since 2516035499b9 ("mm, thp: remove __GFP_NORETRY from khugepaged and madvised allocations"). We have used an explicit __GFP_NORETRY previously which ruled the OOM killer automagically.

Memcg charge path should be semantically compliant with the allocation path and that means that if we do not trigger the OOM killer for costly orders which should do the same in the memcg charge path as well. Otherwise we are forcing callers to distinguish the two and use different gfp masks which is both non-intuitive and bug prone. As soon as we get a costly high order kmalloc user we even do not have any means to tell the memcg specific gfp mask to prevent from OOM because the charging is deep within guts of the slab allocator.

The unexpected memcg OOM on THP has already been fixed upstream by 9d3c3354bb85 ("mm, thp: do not cause memcg oom for thp") but this is one-off fix rather than a generic solution. Teach mem_cgroup_oom to bail out on costly order requests to fix the THP issue as well as any other costly OOM eligible allocations to be added in future.

Also revert 9d3c3354bb85 because special gfp for THP is no longer needed.

---

Hi Andrew,
I have posted core of this patch here [1]. This version just reverts 2516035499b9 on top. I think that we should aim either the next merge window or keep the patch in the mmotm for the 4.18 merge window. I do not have a strong preference. 2516035499b9 acts as a stop gap fix for the time being.

[1] http://lkml.kernel.org/r/[email protected]

 mm/huge_memory.c | 5 ++---
 mm/khugepaged.c  | 8 ++------
 mm/memcontrol.c  | 2 +-
 3 files changed, 5 insertions(+), 10 deletions(-)

index 2297dd9cc7c3..0cc62405de9c 100644
@@ -555,8 +555,7 @@ static int __do_huge_pmd_anonymous_page(struct vm_fault *vmf, struct page *page,
 
 	VM_BUG_ON_PAGE(!PageCompound(page), page);
 
-	if (mem_cgroup_try_charge(page, vma->vm_mm, gfp | __GFP_NORETRY, &memcg,
-				  true)) {
+	if (mem_cgroup_try_charge(page, vma->vm_mm, gfp, &memcg, true)) {
 		put_page(page);
 		count_vm_event(THP_FAULT_FALLBACK);
 		return VM_FAULT_FALLBACK;

@@ -1317,7 +1316,7 @@ int do_huge_pmd_wp_page(struct vm_fault *vmf, pmd_t orig_pmd)
 	}
 
 	if (unlikely(mem_cgroup_try_charge(new_page, vma->vm_mm,
-				huge_gfp | __GFP_NORETRY, &memcg, true))) {
+					huge_gfp, &memcg, true))) {
 		put_page(new_page);
 		split_huge_pmd(vma, vmf->pmd, vmf->address);
 		if (page)

index 214e614b62b0..b7e2268dfc9a 100644
@@ -960,9 +960,7 @@ static void collapse_huge_page(struct mm_struct *mm,
 		goto out_nolock;
 	}
 
-	/* Do not oom kill for khugepaged charges */
-	if (unlikely(mem_cgroup_try_charge(new_page, mm, gfp | __GFP_NORETRY,
-					   &memcg, true))) {
+	if (unlikely(mem_cgroup_try_charge(new_page, mm, gfp, &memcg, true))) {
 		result = SCAN_CGROUP_CHARGE_FAIL;
 		goto out_nolock;
 	}

@@ -1321,9 +1319,7 @@ static void collapse_shmem(struct mm_struct *mm,
 		goto out;
 	}
 
-	/* Do not oom kill for khugepaged charges */
-	if (unlikely(mem_cgroup_try_charge(new_page, mm, gfp | __GFP_NORETRY,
-					   &memcg, true))) {
+	if (unlikely(mem_cgroup_try_charge(new_page, mm, gfp, &memcg, true))) {
 		result = SCAN_CGROUP_CHARGE_FAIL;
 		goto out;
 	}

index d1a917b5b7b7..08accbcd1a18 100644
@@ -1493,7 +1493,7 @@ static void memcg_oom_recover(struct mem_cgroup *memcg)
 
 static void mem_cgroup_oom(struct mem_cgroup *memcg, gfp_t mask, int order)
 {
-	if (!current->memcg_may_oom)
+	if (!current->memcg_may_oom || order > PAGE_ALLOC_COSTLY_ORDER)
 		return;
 	/*
 	 * We are in the middle of the charge context here, so we

2.16.3

Hi,

[This is an automated email]

This commit has been processed because it contains a "Fixes:" tag,
fixing commit: 2516035499b9 mm, thp: remove __GFP_NORETRY from khugepaged and madvised allocations.

The bot has also determined it's probably a bug fixing patch. (score: 12.0224)

The bot has tested the following trees: v4.16, v4.15.15, v4.14.32, v4.9.92.

v4.16: Build OK!
v4.15.15: Build OK!
v4.14.32: Build OK!
v4.9.92: Build OK!

--
Thanks,
Sasha

This has been already handled in older kernels by 9d3c3354bb85 mentioned in the changelog.

Michal Hocko
SUSE Labs