Messages in this thread | | | Date | Wed, 18 Mar 2015 15:34:50 +0100 | From | Vlastimil Babka <> | Subject | Re: [PATCH] mm, memcg: sync allocation and memcg charge gfp flags for THP |
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On 03/16/2015 03:08 PM, Michal Hocko wrote: > memcg currently uses hardcoded GFP_TRANSHUGE gfp flags for all THP > charges. THP allocations, however, might be using different flags > depending on /sys/kernel/mm/transparent_hugepage/{,khugepaged/}defrag > and the current allocation context. > > The primary difference is that defrag configured to "madvise" value will > clear __GFP_WAIT flag from the core gfp mask to make the allocation > lighter for all mappings which are not backed by VM_HUGEPAGE vmas. > If memcg charge path ignores this fact we will get light allocation but > the a potential memcg reclaim would kill the whole point of the > configuration. > > Fix the mismatch by providing the same gfp mask used for the > allocation to the charge functions. This is quite easy for all > paths except for hugepaged kernel thread with !CONFIG_NUMA which is > doing a pre-allocation long before the allocated page is used in > collapse_huge_page via khugepaged_alloc_page. To prevent from cluttering > the whole code path from khugepaged_do_scan we simply return the current > flags as per khugepaged_defrag() value which might have changed since > the preallocation. If somebody changed the value of the knob we would > charge differently but this shouldn't happen often and it is definitely > not critical because it would only lead to a reduced success rate of > one-off THP promotion. > > Signed-off-by: Michal Hocko <mhocko@suse.cz>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
(a nitpick below)
> --- > mm/huge_memory.c | 36 ++++++++++++++++++++---------------- > 1 file changed, 20 insertions(+), 16 deletions(-) > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index 625eb556b509..91898b010406 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -708,7 +708,7 @@ static inline pmd_t mk_huge_pmd(struct page *page, pgprot_t prot) > static int __do_huge_pmd_anonymous_page(struct mm_struct *mm, > struct vm_area_struct *vma, > unsigned long haddr, pmd_t *pmd, > - struct page *page) > + struct page *page, gfp_t gfp) > { > struct mem_cgroup *memcg; > pgtable_t pgtable; > @@ -716,7 +716,7 @@ static int __do_huge_pmd_anonymous_page(struct mm_struct *mm, > > VM_BUG_ON_PAGE(!PageCompound(page), page); > > - if (mem_cgroup_try_charge(page, mm, GFP_TRANSHUGE, &memcg)) > + if (mem_cgroup_try_charge(page, mm, gfp, &memcg)) > return VM_FAULT_OOM; > > pgtable = pte_alloc_one(mm, haddr); > @@ -822,7 +822,7 @@ int do_huge_pmd_anonymous_page(struct mm_struct *mm, struct vm_area_struct *vma, > count_vm_event(THP_FAULT_FALLBACK); > return VM_FAULT_FALLBACK; > } > - if (unlikely(__do_huge_pmd_anonymous_page(mm, vma, haddr, pmd, page))) { > + if (unlikely(__do_huge_pmd_anonymous_page(mm, vma, haddr, pmd, page, gfp))) { > put_page(page); > count_vm_event(THP_FAULT_FALLBACK); > return VM_FAULT_FALLBACK; > @@ -1080,6 +1080,7 @@ int do_huge_pmd_wp_page(struct mm_struct *mm, struct vm_area_struct *vma, > unsigned long haddr; > unsigned long mmun_start; /* For mmu_notifiers */ > unsigned long mmun_end; /* For mmu_notifiers */ > + gfp_t huge_gfp = GFP_TRANSHUGE; /* for allocation and charge */
This value is actually never used. Is it here because the compiler emits a spurious non-initialized value warning otherwise? It should be easy for it to prove that setting new_page to something non-null implies initializing huge_gfp (in the hunk below), and NULL new_page means it doesn't reach the mem_cgroup_try_charge() call?
> > ptl = pmd_lockptr(mm, pmd); > VM_BUG_ON_VMA(!vma->anon_vma, vma); > @@ -1106,10 +1107,8 @@ int do_huge_pmd_wp_page(struct mm_struct *mm, struct vm_area_struct *vma, > alloc: > if (transparent_hugepage_enabled(vma) && > !transparent_hugepage_debug_cow()) { > - gfp_t gfp; > - > - gfp = alloc_hugepage_gfpmask(transparent_hugepage_defrag(vma), 0); > - new_page = alloc_hugepage_vma(gfp, vma, haddr, HPAGE_PMD_ORDER); > + huge_gfp = alloc_hugepage_gfpmask(transparent_hugepage_defrag(vma), 0); > + new_page = alloc_hugepage_vma(huge_gfp, vma, haddr, HPAGE_PMD_ORDER); > } else > new_page = NULL; > > @@ -1131,7 +1130,7 @@ alloc: > } > > if (unlikely(mem_cgroup_try_charge(new_page, mm, > - GFP_TRANSHUGE, &memcg))) { > + huge_gfp, &memcg))) { > put_page(new_page); > if (page) { > split_huge_page(page);
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