On 23/07/2024 23:07, Barry Song wrote: > On Fri, Jul 19, 2024 at 8:56 PM Ryan Roberts <ryan.roberts@xxxxxxx> wrote: >> >> 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? > > Ryan, my question is whether exporting __filemap_alloc_folio_noprof() might lead > to situations where people call __filemap_alloc_folio_noprof() and > forget to call > count_mthp_stat(order, MTHP_STAT_FILE_FALLBACK). Currently, it seems > that counting is always necessary? OK to make sure I've understood, I think you are saying that there is a risk that people will call __filemap_alloc_folio_noprof() and bypass the stat counting? But its the same problem with all "_noprof" functions; if those are called directly, it bypasses the memory allocation profiling infrastructure. So this just needs to be a case of "don't do that" IMHO. filemap_alloc_folio() is the public API. > Another option is that we still > call count mthp > within filemap_alloc_folio_noprof() and make it noinline if > __filemap_alloc_folio_noprof() > is not inline? I could certainly make filemap_alloc_folio_noprof() always out-of-line and then handle the counting privately in the compilation unit. But before my change filemap_alloc_folio_noprof() was inline for the !CONFIG_NUMA case and I was trying not to change that. I think what you're suggesting would be tidier though. I'll make the change. But I don't think it solves the wider problem of the possibility that people can call private APIs. That's what review is for. Thanks, Ryan > >> >>> >>>> + >>>> #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