From: David Hildenbrand <david@redhat.com>
To: Kefeng Wang <wangkefeng.wang@huawei.com>,
Andrew Morton <akpm@linux-foundation.org>
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>,
linux-mm@kvack.org, linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH rfc 3/4] mm: filemap: move __lruvec_stat_mod_folio() out of filemap_set_pte_range()
Date: Wed, 8 May 2024 13:27:33 +0200 [thread overview]
Message-ID: <ecb4f35e-7ead-4674-b934-1de03e1f8c0a@redhat.com> (raw)
In-Reply-To: <609abbe8-cf88-4145-b1d0-397c980aff28@huawei.com>
On 08.05.24 13:15, Kefeng Wang wrote:
>
>
> On 2024/5/8 17:33, David Hildenbrand wrote:
>> On 07.05.24 15:12, Kefeng Wang wrote:
>>>
>>>
>>> On 2024/5/7 19:11, David Hildenbrand wrote:
>>>> On 29.04.24 09:24, Kefeng Wang wrote:
>>>>> Adding __folio_add_file_rmap_ptes() which don't update lruvec stat, it
>>>>> is used in filemap_set_pte_range(), with it, lruvec stat updating is
>>>>> moved into the caller, no functional changes.
>>>>>
>>>>> Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
>>>>> ---
>>>>> include/linux/rmap.h | 2 ++
>>>>> mm/filemap.c | 27 ++++++++++++++++++---------
>>>>> mm/rmap.c | 16 ++++++++++++++++
>>>>> 3 files changed, 36 insertions(+), 9 deletions(-)
>>>>>
>>>>> diff --git a/include/linux/rmap.h b/include/linux/rmap.h
>>>>> index 7229b9baf20d..43014ddd06f9 100644
>>>>> --- a/include/linux/rmap.h
>>>>> +++ b/include/linux/rmap.h
>>>>> @@ -242,6 +242,8 @@ void folio_add_anon_rmap_pmd(struct folio *,
>>>>> struct page *,
>>>>> struct vm_area_struct *, unsigned long address, rmap_t
>>>>> flags);
>>>>> void folio_add_new_anon_rmap(struct folio *, struct
>>>>> vm_area_struct *,
>>>>> unsigned long address);
>>>>> +int __folio_add_file_rmap_ptes(struct folio *, struct page *, int
>>>>> nr_pages,
>>>>> + struct vm_area_struct *);
>>>>> void folio_add_file_rmap_ptes(struct folio *, struct page *, int
>>>>> nr_pages,
>>>>> struct vm_area_struct *);
>>>>> #define folio_add_file_rmap_pte(folio, page, vma) \
>>>>> diff --git a/mm/filemap.c b/mm/filemap.c
>>>>> index 7019692daddd..3966b6616d02 100644
>>>>> --- a/mm/filemap.c
>>>>> +++ b/mm/filemap.c
>>>>> @@ -3501,14 +3501,15 @@ static struct folio
>>>>> *next_uptodate_folio(struct xa_state *xas,
>>>>> static void filemap_set_pte_range(struct vm_fault *vmf, struct folio
>>>>> *folio,
>>>>> struct page *page, unsigned int nr, unsigned long addr,
>>>>> - unsigned long *rss)
>>>>> + unsigned long *rss, int *nr_mapped)
>>>>> {
>>>>> struct vm_area_struct *vma = vmf->vma;
>>>>> pte_t entry;
>>>>> entry = prepare_range_pte_entry(vmf, false, folio, page, nr,
>>>>> addr);
>>>>> - folio_add_file_rmap_ptes(folio, page, nr, vma);
>>>>> + *nr_mapped += __folio_add_file_rmap_ptes(folio, page, nr, vma);
>>>>> +
>>>>> set_ptes(vma->vm_mm, addr, vmf->pte, entry, nr);
>>>>> /* no need to invalidate: a not-present page won't be cached */
>>>>> @@ -3525,7 +3526,8 @@ static void filemap_set_pte_range(struct
>>>>> vm_fault *vmf, struct folio *folio,
>>>>> static vm_fault_t filemap_map_folio_range(struct vm_fault *vmf,
>>>>> struct folio *folio, unsigned long start,
>>>>> unsigned long addr, unsigned int nr_pages,
>>>>> - unsigned long *rss, unsigned int *mmap_miss)
>>>>> + unsigned long *rss, int *nr_mapped,
>>>>> + unsigned int *mmap_miss)
>>>>> {
>>>>> vm_fault_t ret = 0;
>>>>> struct page *page = folio_page(folio, start);
>>>>> @@ -3558,7 +3560,8 @@ static vm_fault_t filemap_map_folio_range(struct
>>>>> vm_fault *vmf,
>>>>> continue;
>>>>> skip:
>>>>> if (count) {
>>>>> - filemap_set_pte_range(vmf, folio, page, count, addr, rss);
>>>>> + filemap_set_pte_range(vmf, folio, page, count, addr,
>>>>> + rss, nr_mapped);
>>>>> if (in_range(vmf->address, addr, count * PAGE_SIZE))
>>>>> ret = VM_FAULT_NOPAGE;
>>>>> }
>>>>> @@ -3571,7 +3574,8 @@ static vm_fault_t filemap_map_folio_range(struct
>>>>> vm_fault *vmf,
>>>>> } while (--nr_pages > 0);
>>>>> if (count) {
>>>>> - filemap_set_pte_range(vmf, folio, page, count, addr, rss);
>>>>> + filemap_set_pte_range(vmf, folio, page, count, addr, rss,
>>>>> + nr_mapped);
>>>>> if (in_range(vmf->address, addr, count * PAGE_SIZE))
>>>>> ret = VM_FAULT_NOPAGE;
>>>>> }
>>>>> @@ -3583,7 +3587,7 @@ static vm_fault_t filemap_map_folio_range(struct
>>>>> vm_fault *vmf,
>>>>> static vm_fault_t filemap_map_order0_folio(struct vm_fault *vmf,
>>>>> struct folio *folio, unsigned long addr,
>>>>> - unsigned long *rss, unsigned int *mmap_miss)
>>>>> + unsigned long *rss, int *nr_mapped, unsigned int *mmap_miss)
>>>>> {
>>>>> vm_fault_t ret = 0;
>>>>> struct page *page = &folio->page;
>>>>> @@ -3606,7 +3610,7 @@ static vm_fault_t
>>>>> filemap_map_order0_folio(struct vm_fault *vmf,
>>>>> if (vmf->address == addr)
>>>>> ret = VM_FAULT_NOPAGE;
>>>>> - filemap_set_pte_range(vmf, folio, page, 1, addr, rss);
>>>>> + filemap_set_pte_range(vmf, folio, page, 1, addr, rss, nr_mapped);
>>>>> return ret;
>>>>> }
>>>>> @@ -3646,6 +3650,7 @@ vm_fault_t filemap_map_pages(struct vm_fault
>>>>> *vmf,
>>>>> folio_type = mm_counter_file(folio);
>>>>> do {
>>>>> unsigned long end;
>>>>> + int nr_mapped = 0;
>>>>> addr += (xas.xa_index - last_pgoff) << PAGE_SHIFT;
>>>>> vmf->pte += xas.xa_index - last_pgoff;
>>>>> @@ -3655,11 +3660,15 @@ vm_fault_t filemap_map_pages(struct vm_fault
>>>>> *vmf,
>>>>> if (!folio_test_large(folio))
>>>>> ret |= filemap_map_order0_folio(vmf,
>>>>> - folio, addr, &rss, &mmap_miss);
>>>>> + folio, addr, &rss, &nr_mapped,
>>>>> + &mmap_miss);
>>>>> else
>>>>> ret |= filemap_map_folio_range(vmf, folio,
>>>>> xas.xa_index - folio->index, addr,
>>>>> - nr_pages, &rss, &mmap_miss);
>>>>> + nr_pages, &rss, &nr_mapped,
>>>>> + &mmap_miss);
>>>>> +
>>>>> + __lruvec_stat_mod_folio(folio, NR_FILE_MAPPED, nr_mapped);
>>>>> folio_unlock(folio);
>>>>> folio_put(folio);
>>>>> diff --git a/mm/rmap.c b/mm/rmap.c
>>>>> index 2608c40dffad..55face4024f2 100644
>>>>> --- a/mm/rmap.c
>>>>> +++ b/mm/rmap.c
>>>>> @@ -1452,6 +1452,22 @@ static __always_inline void
>>>>> __folio_add_file_rmap(struct folio *folio,
>>>>> mlock_vma_folio(folio, vma);
>>>>> }
>>>>> +int __folio_add_file_rmap_ptes(struct folio *folio, struct page *page,
>>>>> + int nr_pages, struct vm_area_struct *vma)
>>>>> +{
>>>>> + int nr, nr_pmdmapped = 0;
>>>>> +
>>>>> + VM_WARN_ON_FOLIO(folio_test_anon(folio), folio);
>>>>> +
>>>>> + nr = __folio_add_rmap(folio, page, nr_pages, RMAP_LEVEL_PTE,
>>>>> + &nr_pmdmapped);
>>>>> +
>>>>> + /* See comments in folio_add_anon_rmap_*() */
>>>>> + if (!folio_test_large(folio))
>>>>> + mlock_vma_folio(folio, vma);
>>>>> +
>>>>> + return nr;
>>>>> +}
>>>>
>>>> I'm not really a fan :/ It does make the code more complicated, and it
>>>> will be harder to extend if we decide to ever account differently (e.g.,
>>>> NR_SHMEM_MAPPED, additional tracking for mTHP etc).
>>>
>>> If more different accounts, this may lead to bad scalability.
>>
>> We already do it for PMD mappings.
>>
>>>>
>>>> With large folios we'll be naturally batching already here, and I do
>>>
>>> Yes, it is batched with large folios，but our fs is ext4/tmpfs, there
>>> are not support large folio or still upstreaming.
>>
>> Okay, so that will be sorted out sooner or later.
>>
>>>
>>>> wonder, if this is really worth for performance, or if we could find
>>>> another way of batching (let the caller activate batching and drain
>>>> afterwards) without exposing these details to the caller.
>>>
>>> It does reduce latency when batch lruvec stat updating without large
>>> folio, but I can't find better way, or let's wait for the large folio
>>> support on ext4/tmpfs, I also Cced memcg maintainers in patch4 to see if
>>> there are any other ideas.
>>
>> I'm not convinced this benefit here is worth making the code more
>> complicated.
>>
>> Maybe we can find another way to optimize this batching in rmap code
>> without having to leak these details to the callers.
>>
>> For example, we could pass an optional batching structure to all rmap
>> add/rel functions that would collect these stat updates. Then we could
>> have one function to flush it and update the counters combined.
>>
>> Such batching could be beneficial also for page unmapping/zapping where
>> we might unmap various different folios in one go.
>
> It sounds better and clearer, I will try it and see the results, thanks
> for your advise!
To batch across multiple folios, it might be sufficient to remember in
the batching structure for now:
* folio_memcg(folio)
* folio_pgdat(folio)
* NR_ANON_MAPPED diff
* NR_FILE_MAPPED diff
If the memcg of pgdat would change, we simply flush. Otherwise we batch
and the caller flushes.
Likely we mapping/unmapping multiple folios they belong to the same
pgdat+memcg.
The only tricky bit is the rcu_read_lock() around folio_memcg(); that
might require some thought.
Hm ....
--
Cheers,
David / dhildenb
next prev parent reply other threads:[~2024-05-08 11:27 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-29 7:24 [PATCH rfc 0/4] mm: filemap: try to batch lruvec stat updating Kefeng Wang
2024-04-29 7:24 ` [PATCH rfc 1/4] mm: memory: add prepare_range_pte_entry() Kefeng Wang
2024-04-29 7:24 ` [PATCH rfc 2/4] mm: filemap: add filemap_set_pte_range() Kefeng Wang
2024-04-29 7:24 ` [PATCH rfc 3/4] mm: filemap: move __lruvec_stat_mod_folio() out of filemap_set_pte_range() Kefeng Wang
2024-05-07 11:11 ` David Hildenbrand
2024-05-07 13:12 ` Kefeng Wang
2024-05-08 9:33 ` David Hildenbrand
2024-05-08 11:15 ` Kefeng Wang
2024-05-08 11:27 ` David Hildenbrand [this message]
2024-05-08 13:56 ` Kefeng Wang
2024-04-29 7:24 ` [PATCH rfc 4/4] mm: filemap: try to batch lruvec stat updating Kefeng Wang
2024-05-07 9:06 ` Kefeng Wang
2024-05-09 14:01 ` Johannes Weiner
2024-05-10 1:55 ` Kefeng Wang
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