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SubjectRe: [patch 2/2] mm, thp: track fallbacks due to failed memcg charges separately
On Fri, Mar 06, 2020 at 02:22:35PM -0800, David Rientjes wrote:
> The thp_fault_fallback and thp_file_fallback vmstats are incremented if
> either the hugepage allocation fails through the page allocator or the
> hugepage charge fails through mem cgroup.
>
> This patch leaves this field untouched but adds two new fields,
> thp_{fault,file}_fallback_charge, which is incremented only when the mem
> cgroup charge fails.
>
> This distinguishes between attempted hugepage allocations that fail due to
> fragmentation (or low memory conditions) and those that fail due to mem
> cgroup limits. That can be used to determine the impact of fragmentation
> on the system by excluding faults that failed due to memcg usage.
>
> Signed-off-by: David Rientjes <rientjes@google.com>

Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> ---
> Documentation/admin-guide/mm/transhuge.rst | 10 ++++++++++
> include/linux/vm_event_item.h | 3 +++
> mm/huge_memory.c | 2 ++
> mm/shmem.c | 4 +++-
> mm/vmstat.c | 2 ++
> 5 files changed, 20 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/admin-guide/mm/transhuge.rst b/Documentation/admin-guide/mm/transhuge.rst
> --- a/Documentation/admin-guide/mm/transhuge.rst
> +++ b/Documentation/admin-guide/mm/transhuge.rst
> @@ -310,6 +310,11 @@ thp_fault_fallback
> is incremented if a page fault fails to allocate
> a huge page and instead falls back to using small pages.
>
> +thp_fault_fallback_charge
> + is incremented if a page fault fails to charge a huge page and
> + instead falls back to using small pages even though the
> + allocation was successful.
> +
> thp_collapse_alloc_failed
> is incremented if khugepaged found a range
> of pages that should be collapsed into one huge page but failed
> @@ -323,6 +328,11 @@ thp_file_fallback
> is incremented if a file huge page is attempted to be allocated
> but fails and instead falls back to using small pages.
>
> +thp_file_fallback_charge
> + is incremented if a file huge page cannot be charged and instead
> + falls back to using small pages even though the allocation was
> + successful.
> +
> thp_file_mapped
> is incremented every time a file huge page is mapped into
> user address space.
> diff --git a/include/linux/vm_event_item.h b/include/linux/vm_event_item.h
> --- a/include/linux/vm_event_item.h
> +++ b/include/linux/vm_event_item.h
> @@ -73,10 +73,12 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT,
> #ifdef CONFIG_TRANSPARENT_HUGEPAGE
> THP_FAULT_ALLOC,
> THP_FAULT_FALLBACK,
> + THP_FAULT_FALLBACK_CHARGE,
> THP_COLLAPSE_ALLOC,
> THP_COLLAPSE_ALLOC_FAILED,
> THP_FILE_ALLOC,
> THP_FILE_FALLBACK,
> + THP_FILE_FALLBACK_CHARGE,
> THP_FILE_MAPPED,
> THP_SPLIT_PAGE,
> THP_SPLIT_PAGE_FAILED,
> @@ -117,6 +119,7 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT,
> #ifndef CONFIG_TRANSPARENT_HUGEPAGE
> #define THP_FILE_ALLOC ({ BUILD_BUG(); 0; })
> #define THP_FILE_FALLBACK ({ BUILD_BUG(); 0; })
> +#define THP_FILE_FALLBACK_CHARGE ({ BUILD_BUG(); 0; })
> #define THP_FILE_MAPPED ({ BUILD_BUG(); 0; })
> #endif
>
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -597,6 +597,7 @@ static vm_fault_t __do_huge_pmd_anonymous_page(struct vm_fault *vmf,
> if (mem_cgroup_try_charge_delay(page, vma->vm_mm, gfp, &memcg, true)) {
> put_page(page);
> count_vm_event(THP_FAULT_FALLBACK);
> + count_vm_event(THP_FAULT_FALLBACK_CHARGE);
> return VM_FAULT_FALLBACK;
> }
>
> @@ -1406,6 +1407,7 @@ vm_fault_t do_huge_pmd_wp_page(struct vm_fault *vmf, pmd_t orig_pmd)
> put_page(page);
> ret |= VM_FAULT_FALLBACK;
> count_vm_event(THP_FAULT_FALLBACK);
> + count_vm_event(THP_FAULT_FALLBACK_CHARGE);
> goto out;
> }
>
> diff --git a/mm/shmem.c b/mm/shmem.c
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -1871,8 +1871,10 @@ static int shmem_getpage_gfp(struct inode *inode, pgoff_t index,
> error = mem_cgroup_try_charge_delay(page, charge_mm, gfp, &memcg,
> PageTransHuge(page));
> if (error) {
> - if (PageTransHuge(page))
> + if (PageTransHuge(page)) {
> count_vm_event(THP_FILE_FALLBACK);
> + count_vm_event(THP_FILE_FALLBACK_CHARGE);
> + }
> goto unacct;
> }
> error = shmem_add_to_page_cache(page, mapping, hindex,
> diff --git a/mm/vmstat.c b/mm/vmstat.c
> --- a/mm/vmstat.c
> +++ b/mm/vmstat.c
> @@ -1254,10 +1254,12 @@ const char * const vmstat_text[] = {
> #ifdef CONFIG_TRANSPARENT_HUGEPAGE
> "thp_fault_alloc",
> "thp_fault_fallback",
> + "thp_fault_fallback_charge",
> "thp_collapse_alloc",
> "thp_collapse_alloc_failed",
> "thp_file_alloc",
> "thp_file_fallback",
> + "thp_file_fallback_charge",
> "thp_file_mapped",
> "thp_split_page",
> "thp_split_page_failed",

--
Kirill A. Shutemov

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