On Fri, Mar 6, 2020 at 2:22 PM David Rientjes <rientjes@xxxxxxxxxx> wrote:
>
> The existing thp_fault_fallback indicates when thp attempts to allocate a
> hugepage but fails, or if the hugepage cannot be charged to the mem cgroup
> hierarchy.
>
> Extend this to shmem as well. Adds a new thp_file_fallback to complement
> thp_file_alloc that gets incremented when a hugepage is attempted to be
> allocated but fails, or if it cannot be charged to the mem cgroup
> hierarchy.
>
> Additionally, remove the check for CONFIG_TRANSPARENT_HUGE_PAGECACHE from
> shmem_alloc_hugepage() since it is only called with this configuration
> option.
Looks good to me. Thanks for taking this suggestion. Reviewed-by: Yang
Shi <yang.shi@xxxxxxxxxxxxxxxxx>
>
> Signed-off-by: David Rientjes <rientjes@xxxxxxxxxx>
> ---
> Documentation/admin-guide/mm/transhuge.rst | 4 ++++
> include/linux/vm_event_item.h | 2 ++
> mm/shmem.c | 10 ++++++----
> mm/vmstat.c | 1 +
> 4 files changed, 13 insertions(+), 4 deletions(-)
>
> 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
> @@ -319,6 +319,10 @@ thp_file_alloc
> is incremented every time a file huge page is successfully
> allocated.
>
> +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_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
> @@ -76,6 +76,7 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT,
> THP_COLLAPSE_ALLOC,
> THP_COLLAPSE_ALLOC_FAILED,
> THP_FILE_ALLOC,
> + THP_FILE_FALLBACK,
> THP_FILE_MAPPED,
> THP_SPLIT_PAGE,
> THP_SPLIT_PAGE_FAILED,
> @@ -115,6 +116,7 @@ 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_MAPPED ({ BUILD_BUG(); 0; })
> #endif
>
> diff --git a/mm/shmem.c b/mm/shmem.c
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -1472,9 +1472,6 @@ static struct page *shmem_alloc_hugepage(gfp_t gfp,
> pgoff_t hindex;
> struct page *page;
>
> - if (!IS_ENABLED(CONFIG_TRANSPARENT_HUGE_PAGECACHE))
> - return NULL;
> -
> hindex = round_down(index, HPAGE_PMD_NR);
> if (xa_find(&mapping->i_pages, &hindex, hindex + HPAGE_PMD_NR - 1,
> XA_PRESENT))
> @@ -1486,6 +1483,8 @@ static struct page *shmem_alloc_hugepage(gfp_t gfp,
> shmem_pseudo_vma_destroy(&pvma);
> if (page)
> prep_transhuge_page(page);
> + else
> + count_vm_event(THP_FILE_FALLBACK);
> return page;
> }
>
> @@ -1871,8 +1870,11 @@ 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 (error) {
> + if (PageTransHuge(page))
> + count_vm_event(THP_FILE_FALLBACK);
> goto unacct;
> + }
> error = shmem_add_to_page_cache(page, mapping, hindex,
> NULL, gfp & GFP_RECLAIM_MASK);
> if (error) {
> diff --git a/mm/vmstat.c b/mm/vmstat.c
> --- a/mm/vmstat.c
> +++ b/mm/vmstat.c
> @@ -1257,6 +1257,7 @@ const char * const vmstat_text[] = {
> "thp_collapse_alloc",
> "thp_collapse_alloc_failed",
> "thp_file_alloc",
> + "thp_file_fallback",
> "thp_file_mapped",
> "thp_split_page",
> "thp_split_page_failed",
