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[2003:cb:c713:2a00:f151:50f1:7164:32e6]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4290c739083sm9738815e9.18.2024.08.08.01.17.10 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 08 Aug 2024 01:17:11 -0700 (PDT) Message-ID: <41b49313-5804-46ba-9e1d-358b079274cd@redhat.com> Date: Thu, 8 Aug 2024 10:17:10 +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> <14128caf-f7dc-41c0-ab63-c8d434c35f76@redhat.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 10:08, David Hildenbrand wrote: > 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). > Sorry that I am talking to myself: I'm wondering if we also have to adjust the counter when splitting a large folio to multiple smaller-but-still-large folios. -- Cheers, David / dhildenb