On 19/07/2024 01:12, Barry Song wrote: > On Wed, Jul 17, 2024 at 1:59 AM Ryan Roberts <ryan.roberts@xxxxxxx> wrote: >> >> Expose 3 new mTHP stats for file (pagecache) folio allocations: >> >> /sys/kernel/mm/transparent_hugepage/hugepages-*kB/stats/file_alloc >> /sys/kernel/mm/transparent_hugepage/hugepages-*kB/stats/file_fallback >> /sys/kernel/mm/transparent_hugepage/hugepages-*kB/stats/file_fallback_charge >> >> This will provide some insight on the sizes of large folios being >> allocated for file-backed memory, and how often allocation is failing. >> >> All non-order-0 (and most order-0) folio allocations are currently done >> through filemap_alloc_folio(), and folios are charged in a subsequent >> call to filemap_add_folio(). So count file_fallback when allocation >> fails in filemap_alloc_folio() and count file_alloc or >> file_fallback_charge in filemap_add_folio(), based on whether charging >> succeeded or not. There are some users of filemap_add_folio() that >> allocate their own order-0 folio by other means, so we would not count >> an allocation failure in this case, but we also don't care about order-0 >> allocations. This approach feels like it should be good enough and >> doesn't require any (impractically large) refactoring. >> >> The existing mTHP stats interface is reused to provide consistency to >> users. And because we are reusing the same interface, we can reuse the >> same infrastructure on the kernel side. >> >> Signed-off-by: Ryan Roberts <ryan.roberts@xxxxxxx> >> --- >> Documentation/admin-guide/mm/transhuge.rst | 13 +++++++++++++ >> include/linux/huge_mm.h | 3 +++ >> include/linux/pagemap.h | 16 ++++++++++++++-- >> mm/filemap.c | 6 ++++-- >> mm/huge_memory.c | 7 +++++++ >> 5 files changed, 41 insertions(+), 4 deletions(-) >> >> diff --git a/Documentation/admin-guide/mm/transhuge.rst b/Documentation/admin-guide/mm/transhuge.rst >> index 058485daf186..d4857e457add 100644 >> --- a/Documentation/admin-guide/mm/transhuge.rst >> +++ b/Documentation/admin-guide/mm/transhuge.rst >> @@ -512,6 +512,19 @@ shmem_fallback_charge >> falls back to using small pages even though the allocation was >> successful. >> >> +file_alloc >> + is incremented every time a file huge page is successfully >> + allocated. >> + >> +file_fallback >> + is incremented if a file huge page is attempted to be allocated >> + but fails and instead falls back to using small pages. >> + >> +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. >> + > > I realized that when we talk about fallback, it doesn't necessarily mean > small pages; it could also refer to smaller huge pages. Yes good point, I'll update the documentation to reflect that for all memory types. > > anon_fault_alloc > is incremented every time a huge page is successfully > allocated and charged to handle a page fault. > > anon_fault_fallback > is incremented if a page fault fails to allocate or charge > a huge page and instead falls back to using huge pages with > lower orders or small pages. > > anon_fault_fallback_charge > is incremented if a page fault fails to charge a huge page and > instead falls back to using huge pages with lower orders or > small pages even though the allocation was successful. > > This also applies to files, right? It does in the place you highlight below, but page_cache_ra_order() just falls back immediately to order-0. Regardless, I think we should just document the user facing docs to allow for a lower high order. That gives the implementation more flexibility. > > do { > gfp_t alloc_gfp = gfp; > > err = -ENOMEM; > if (order > 0) > alloc_gfp |= __GFP_NORETRY | __GFP_NOWARN; > folio = filemap_alloc_folio(alloc_gfp, order); > if (!folio) > continue; > > /* Init accessed so avoid atomic > mark_page_accessed later */ > if (fgp_flags & FGP_ACCESSED) > __folio_set_referenced(folio); > > err = filemap_add_folio(mapping, folio, index, gfp); > if (!err) > break; > folio_put(folio); > folio = NULL; > } while (order-- > 0); > > >> split >> is incremented every time a huge page is successfully split into >> smaller orders. This can happen for a variety of reasons but a >> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h >> index b8c63c3e967f..4f9109fcdded 100644 >> --- a/include/linux/huge_mm.h >> +++ b/include/linux/huge_mm.h >> @@ -123,6 +123,9 @@ enum mthp_stat_item { >> MTHP_STAT_SHMEM_ALLOC, >> MTHP_STAT_SHMEM_FALLBACK, >> MTHP_STAT_SHMEM_FALLBACK_CHARGE, >> + MTHP_STAT_FILE_ALLOC, >> + MTHP_STAT_FILE_FALLBACK, >> + MTHP_STAT_FILE_FALLBACK_CHARGE, >> MTHP_STAT_SPLIT, >> MTHP_STAT_SPLIT_FAILED, >> MTHP_STAT_SPLIT_DEFERRED, >> diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h >> index 6e2f72d03176..95a147b5d117 100644 >> --- a/include/linux/pagemap.h >> +++ b/include/linux/pagemap.h >> @@ -562,14 +562,26 @@ static inline void *detach_page_private(struct page *page) >> } >> >> #ifdef CONFIG_NUMA >> -struct folio *filemap_alloc_folio_noprof(gfp_t gfp, unsigned int order); >> +struct folio *__filemap_alloc_folio_noprof(gfp_t gfp, unsigned int order); >> #else >> -static inline struct folio *filemap_alloc_folio_noprof(gfp_t gfp, unsigned int order) >> +static inline struct folio *__filemap_alloc_folio_noprof(gfp_t gfp, unsigned int order) >> { >> return folio_alloc_noprof(gfp, order); >> } >> #endif >> >> +static inline struct folio *filemap_alloc_folio_noprof(gfp_t gfp, unsigned int order) >> +{ >> + struct folio *folio; >> + >> + folio = __filemap_alloc_folio_noprof(gfp, order); >> + >> + if (!folio) >> + count_mthp_stat(order, MTHP_STAT_FILE_FALLBACK); >> + >> + return folio; >> +} > > Do we need to add and export __filemap_alloc_folio_noprof()? It is exported. See the below change in filemap.c. Previously filemap_alloc_folio_noprof() was exported, but that is now an inline and __filemap_alloc_folio_noprof() is exported in its place. > In any case, > we won't call count_mthp_stat(order, MTHP_STAT_FILE_FALLBACK) and > will only allocate the folio instead? Sorry I don't understand what you mean by this? > >> + >> #define filemap_alloc_folio(...) \ >> alloc_hooks(filemap_alloc_folio_noprof(__VA_ARGS__)) >> >> diff --git a/mm/filemap.c b/mm/filemap.c >> index 53d5d0410b51..131d514fca29 100644 >> --- a/mm/filemap.c >> +++ b/mm/filemap.c >> @@ -963,6 +963,8 @@ int filemap_add_folio(struct address_space *mapping, struct folio *folio, >> int ret; >> >> ret = mem_cgroup_charge(folio, NULL, gfp); >> + count_mthp_stat(folio_order(folio), >> + ret ? MTHP_STAT_FILE_FALLBACK_CHARGE : MTHP_STAT_FILE_ALLOC); >> if (ret) >> return ret; > > Would the following be better? > > ret = mem_cgroup_charge(folio, NULL, gfp); > if (ret) { > count_mthp_stat(folio_order(folio), > MTHP_STAT_FILE_FALLBACK_CHARGE); > return ret; > } > count_mthp_stat(folio_order(folio), MTHP_STAT_FILE_ALLOC); > > Anyway, it's up to you. The code just feels a bit off to me :-) Yes, agree your version is better. I also noticed that anon and shmem increment FALLBACK whenever FALLBACK_CHARGE is incremented so I should apply those same semantics here. Thanks, Ryan > >> >> @@ -990,7 +992,7 @@ int filemap_add_folio(struct address_space *mapping, struct folio *folio, >> EXPORT_SYMBOL_GPL(filemap_add_folio); >> >> #ifdef CONFIG_NUMA >> -struct folio *filemap_alloc_folio_noprof(gfp_t gfp, unsigned int order) >> +struct folio *__filemap_alloc_folio_noprof(gfp_t gfp, unsigned int order) >> { >> int n; >> struct folio *folio; >> @@ -1007,7 +1009,7 @@ struct folio *filemap_alloc_folio_noprof(gfp_t gfp, unsigned int order) >> } >> return folio_alloc_noprof(gfp, order); >> } >> -EXPORT_SYMBOL(filemap_alloc_folio_noprof); >> +EXPORT_SYMBOL(__filemap_alloc_folio_noprof); >> #endif >> >> /* >> diff --git a/mm/huge_memory.c b/mm/huge_memory.c >> index 578ac212c172..26d558e3e80f 100644 >> --- a/mm/huge_memory.c >> +++ b/mm/huge_memory.c >> @@ -608,7 +608,14 @@ static struct attribute_group anon_stats_attr_grp = { >> .attrs = anon_stats_attrs, >> }; >> >> +DEFINE_MTHP_STAT_ATTR(file_alloc, MTHP_STAT_FILE_ALLOC); >> +DEFINE_MTHP_STAT_ATTR(file_fallback, MTHP_STAT_FILE_FALLBACK); >> +DEFINE_MTHP_STAT_ATTR(file_fallback_charge, MTHP_STAT_FILE_FALLBACK_CHARGE); >> + >> static struct attribute *file_stats_attrs[] = { >> + &file_alloc_attr.attr, >> + &file_fallback_attr.attr, >> + &file_fallback_charge_attr.attr, >> #ifdef CONFIG_SHMEM >> &shmem_alloc_attr.attr, >> &shmem_fallback_attr.attr, >> -- >> 2.43.0 >> > > Thanks > Barry