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Subject[patch] mm, thp: do not cause memcg oom for thp
Commit 2516035499b9 ("mm, thp: remove __GFP_NORETRY from khugepaged and
madvised allocations") changed the page allocator to no longer detect thp
allocations based on __GFP_NORETRY.

It did not, however, modify the mem cgroup try_charge() path to avoid oom
kill for either khugepaged collapsing or thp faulting. It is never
expected to oom kill a process to allocate a hugepage for thp; reclaim is
governed by the thp defrag mode and MADV_HUGEPAGE, but allocations (and
charging) should fallback instead of oom killing processes.

Fixes: 2516035499b9 ("mm, thp: remove __GFP_NORETRY from khugepaged and madvised allocations")
Signed-off-by: David Rientjes <rientjes@google.com>
---
mm/huge_memory.c | 5 +++--
mm/khugepaged.c | 8 ++++++--
2 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -555,7 +555,8 @@ 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, &memcg, true)) {
+ if (mem_cgroup_try_charge(page, vma->vm_mm, gfp | __GFP_NORETRY, &memcg,
+ true)) {
put_page(page);
count_vm_event(THP_FAULT_FALLBACK);
return VM_FAULT_FALLBACK;
@@ -1316,7 +1317,7 @@ 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, &memcg, true))) {
+ huge_gfp | __GFP_NORETRY, &memcg, true))) {
put_page(new_page);
split_huge_pmd(vma, vmf->pmd, vmf->address);
if (page)
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -960,7 +960,9 @@ static void collapse_huge_page(struct mm_struct *mm,
goto out_nolock;
}

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

- if (unlikely(mem_cgroup_try_charge(new_page, mm, gfp, &memcg, true))) {
+ /* Do not oom kill for khugepaged charges */
+ if (unlikely(mem_cgroup_try_charge(new_page, mm, gfp | __GFP_NORETRY,
+ &memcg, true))) {
result = SCAN_CGROUP_CHARGE_FAIL;
goto out;
}
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