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[2003:cb:c713:2a00:f151:50f1:7164:32e6]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-36d271576c1sm1054827f8f.21.2024.08.08.01.08.41 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 08 Aug 2024 01:08:42 -0700 (PDT) Message-ID: <14128caf-f7dc-41c0-ab63-c8d434c35f76@redhat.com> Date: Thu, 8 Aug 2024 10:08:40 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH RFC 1/2] mm: collect the number of anon large folios From: David Hildenbrand To: Barry Song <21cnbao@gmail.com> Cc: akpm@linux-foundation.org, baolin.wang@linux.alibaba.com, chrisl@kernel.org, hanchuanhua@oppo.com, ioworker0@gmail.com, kaleshsingh@google.com, kasong@tencent.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, ryan.roberts@arm.com, v-songbaohua@oppo.com, ziy@nvidia.com References: <20240808010457.228753-2-21cnbao@gmail.com> <20240808070847.285075-1-21cnbao@gmail.com> Content-Language: en-US Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 08.08.24 10:03, David Hildenbrand wrote: > On 08.08.24 09:08, Barry Song wrote: >> On Thu, Aug 8, 2024 at 1:05 PM Barry Song <21cnbao@gmail.com> wrote: >>> >>> From: Barry Song >>> >>> When a new anonymous mTHP is added to the rmap, we increase the count. >>> We reduce the count whenever an mTHP is completely unmapped. >>> >>> Signed-off-by: Barry Song >>> --- >>> Documentation/admin-guide/mm/transhuge.rst | 5 +++++ >>> include/linux/huge_mm.h | 15 +++++++++++++-- >>> mm/huge_memory.c | 2 ++ >>> mm/rmap.c | 3 +++ >>> 4 files changed, 23 insertions(+), 2 deletions(-) >>> >>> diff --git a/Documentation/admin-guide/mm/transhuge.rst b/Documentation/admin-guide/mm/transhuge.rst >>> index 058485daf186..715f181543f6 100644 >>> --- a/Documentation/admin-guide/mm/transhuge.rst >>> +++ b/Documentation/admin-guide/mm/transhuge.rst >>> @@ -527,6 +527,11 @@ split_deferred >>> it would free up some memory. Pages on split queue are going to >>> be split under memory pressure, if splitting is possible. >>> >>> +anon_num >>> + the number of anon huge pages we have in the whole system. >>> + These huge pages could be still entirely mapped and have partially >>> + unmapped and unused subpages. >>> + >>> As the system ages, allocating huge pages may be expensive as the >>> system uses memory compaction to copy data around memory to free a >>> huge page for use. There are some counters in ``/proc/vmstat`` to help >>> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h >>> index e25d9ebfdf89..294c348fe3cc 100644 >>> --- a/include/linux/huge_mm.h >>> +++ b/include/linux/huge_mm.h >>> @@ -281,6 +281,7 @@ enum mthp_stat_item { >>> MTHP_STAT_SPLIT, >>> MTHP_STAT_SPLIT_FAILED, >>> MTHP_STAT_SPLIT_DEFERRED, >>> + MTHP_STAT_NR_ANON, >>> __MTHP_STAT_COUNT >>> }; >>> >>> @@ -291,14 +292,24 @@ struct mthp_stat { >>> #ifdef CONFIG_SYSFS >>> DECLARE_PER_CPU(struct mthp_stat, mthp_stats); >>> >>> -static inline void count_mthp_stat(int order, enum mthp_stat_item item) >>> +static inline void mod_mthp_stat(int order, enum mthp_stat_item item, int delta) >>> { >>> if (order <= 0 || order > PMD_ORDER) >>> return; >>> >>> - this_cpu_inc(mthp_stats.stats[order][item]); >>> + this_cpu_add(mthp_stats.stats[order][item], delta); >>> +} >>> + >>> +static inline void count_mthp_stat(int order, enum mthp_stat_item item) >>> +{ >>> + mod_mthp_stat(order, item, 1); >>> } >>> + >>> #else >>> +static inline void mod_mthp_stat(int order, enum mthp_stat_item item, int delta) >>> +{ >>> +} >>> + >>> static inline void count_mthp_stat(int order, enum mthp_stat_item item) >>> { >>> } >>> diff --git a/mm/huge_memory.c b/mm/huge_memory.c >>> index 697fcf89f975..b6bc2a3791e3 100644 >>> --- a/mm/huge_memory.c >>> +++ b/mm/huge_memory.c >>> @@ -578,6 +578,7 @@ DEFINE_MTHP_STAT_ATTR(shmem_fallback_charge, MTHP_STAT_SHMEM_FALLBACK_CHARGE); >>> DEFINE_MTHP_STAT_ATTR(split, MTHP_STAT_SPLIT); >>> DEFINE_MTHP_STAT_ATTR(split_failed, MTHP_STAT_SPLIT_FAILED); >>> DEFINE_MTHP_STAT_ATTR(split_deferred, MTHP_STAT_SPLIT_DEFERRED); >>> +DEFINE_MTHP_STAT_ATTR(anon_num, MTHP_STAT_NR_ANON); >>> >>> static struct attribute *stats_attrs[] = { >>> &anon_fault_alloc_attr.attr, >>> @@ -591,6 +592,7 @@ static struct attribute *stats_attrs[] = { >>> &split_attr.attr, >>> &split_failed_attr.attr, >>> &split_deferred_attr.attr, >>> + &anon_num_attr.attr, >>> NULL, >>> }; >>> >>> diff --git a/mm/rmap.c b/mm/rmap.c >>> index 901950200957..2b722f26224c 100644 >>> --- a/mm/rmap.c >>> +++ b/mm/rmap.c >>> @@ -1467,6 +1467,7 @@ void folio_add_new_anon_rmap(struct folio *folio, struct vm_area_struct *vma, >>> } >>> >>> __folio_mod_stat(folio, nr, nr_pmdmapped); >>> + mod_mthp_stat(folio_order(folio), MTHP_STAT_NR_ANON, 1); >>> } >>> >>> static __always_inline void __folio_add_file_rmap(struct folio *folio, >>> @@ -1582,6 +1583,8 @@ static __always_inline void __folio_remove_rmap(struct folio *folio, >>> list_empty(&folio->_deferred_list)) >>> deferred_split_folio(folio); >>> __folio_mod_stat(folio, -nr, -nr_pmdmapped); >>> + if (folio_test_anon(folio) && !atomic_read(mapped)) >> >> could have a risk here two processes unmap at the same time, so >> they both get zero on atomic_read(mapped)? should read the value >> of atomic_dec_return() instead to confirm we are the last one >> doing unmap? > > I would appreciate if we leave the rmap out here. > > Can't we handle that when actually freeing the folio? folio_test_anon() > is sticky until freed. To be clearer: we increment the counter when we set a folio anon, which should indeed only happen in folio_add_new_anon_rmap(). We'll have to ignore hugetlb here where we do it in hugetlb_add_new_anon_rmap(). Then, when we free an anon folio we decrement the counter. (hugetlb should clear the anon flag when an anon folio gets freed back to its allocator -- likely that is already done). -- Cheers, David / dhildenb