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Message-ID: <0f581d0d-3139-4007-2161-592a0a545b50@intel.com>
Date: Fri, 17 Mar 2023 00:27:13 +0800
From: "Yin, Fengwei" <fengwei.yin@...el.com>
To: Ryan Roberts <ryan.roberts@....com>,
"Matthew Wilcox (Oracle)" <willy@...radead.org>,
<linux-arch@...r.kernel.org>
CC: <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 34/36] rmap: add folio_add_file_rmap_range()
Hi Matthew,
On 3/16/2023 12:08 AM, Ryan Roberts wrote:
> On 15/03/2023 13:34, Ryan Roberts wrote:
>> On 15/03/2023 05:14, Matthew Wilcox (Oracle) wrote:
>>> From: Yin Fengwei <fengwei.yin@...el.com>
>>>
>>> folio_add_file_rmap_range() allows to add pte mapping to a specific
>>> range of file folio. Comparing to page_add_file_rmap(), it batched
>>> updates __lruvec_stat for large folio.
>>>
>>> Signed-off-by: Yin Fengwei <fengwei.yin@...el.com>
>>> Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
>>> ---
>>> include/linux/rmap.h | 2 ++
>>> mm/rmap.c | 60 +++++++++++++++++++++++++++++++++-----------
>>> 2 files changed, 48 insertions(+), 14 deletions(-)
>>>
>>> diff --git a/include/linux/rmap.h b/include/linux/rmap.h
>>> index b87d01660412..a3825ce81102 100644
>>> --- a/include/linux/rmap.h
>>> +++ b/include/linux/rmap.h
>>> @@ -198,6 +198,8 @@ void folio_add_new_anon_rmap(struct folio *, struct vm_area_struct *,
>>> unsigned long address);
>>> void page_add_file_rmap(struct page *, struct vm_area_struct *,
>>> bool compound);
>>> +void folio_add_file_rmap_range(struct folio *, struct page *, unsigned int nr,
>>> + struct vm_area_struct *, bool compound);
>>> void page_remove_rmap(struct page *, struct vm_area_struct *,
>>> bool compound);
>>>
>>> diff --git a/mm/rmap.c b/mm/rmap.c
>>> index 4898e10c569a..a91906b28835 100644
>>> --- a/mm/rmap.c
>>> +++ b/mm/rmap.c
>>> @@ -1301,31 +1301,39 @@ void folio_add_new_anon_rmap(struct folio *folio, struct vm_area_struct *vma,
>>> }
>>>
>>> /**
>>> - * page_add_file_rmap - add pte mapping to a file page
>>> - * @page: the page to add the mapping to
>>> + * folio_add_file_rmap_range - add pte mapping to page range of a folio
>>> + * @folio: The folio to add the mapping to
>>> + * @page: The first page to add
>>> + * @nr_pages: The number of pages which will be mapped
>>> * @vma: the vm area in which the mapping is added
>>> * @compound: charge the page as compound or small page
>>> *
>>> + * The page range of folio is defined by [first_page, first_page + nr_pages)
>>> + *
>>> * The caller needs to hold the pte lock.
>>> */
>>> -void page_add_file_rmap(struct page *page, struct vm_area_struct *vma,
>>> - bool compound)
>>> +void folio_add_file_rmap_range(struct folio *folio, struct page *page,
>>> + unsigned int nr_pages, struct vm_area_struct *vma,
>>> + bool compound)
>>> {
>>> - struct folio *folio = page_folio(page);
>>> atomic_t *mapped = &folio->_nr_pages_mapped;
>>> - int nr = 0, nr_pmdmapped = 0;
>>> - bool first;
>>> + unsigned int nr_pmdmapped = 0, first;
>>> + int nr = 0;
>>>
>>> - VM_BUG_ON_PAGE(compound && !PageTransHuge(page), page);
>>> + VM_WARN_ON_FOLIO(compound && !folio_test_pmd_mappable(folio), folio);
>>>
>>> /* Is page being mapped by PTE? Is this its first map to be added? */
>>> if (likely(!compound)) {
>>> - first = atomic_inc_and_test(&page->_mapcount);
>>> - nr = first;
>>> - if (first && folio_test_large(folio)) {
>>> - nr = atomic_inc_return_relaxed(mapped);
>>> - nr = (nr < COMPOUND_MAPPED);
>>> - }
>>> + do {
>>> + first = atomic_inc_and_test(&page->_mapcount);
>>> + if (first && folio_test_large(folio)) {
>>> + first = atomic_inc_return_relaxed(mapped);
>>> + first = (nr < COMPOUND_MAPPED);
>>
>> This still contains the typo that Yin Fengwei spotted in the previous version:
>> https://lore.kernel.org/linux-mm/20230228213738.272178-1-willy@infradead.org/T/#m84673899e25bc31356093a1177941f2cc35e5da8
>>
>> FYI, I'm seeing a perf regression of about 1% when compiling the kernel on
>> Ampere Altra (arm64) with this whole series on top of v6.3-rc1 (In a VM using
>> ext4 filesystem). Looks like instruction aborts are taking much longer and a
>> selection of syscalls are a bit slower. Still hunting down the root cause. Will
>> report once I have conclusive diagnosis.
>
> I'm sorry - I'm struggling to find the exact cause. But its spending over 2x the
> amount of time in the instruction abort handling code once patches 32-36 are
> included. Everything in the flame graph is just taking longer. Perhaps we are
> getting more instruction aborts somehow? I have the flamegraphs if anyone wants
> them - just shout and I'll email them separately.
Thanks a lot to Ryan for sharing the flamegraphs to me. I found the __do_fault()
is called with patch 32-36 while no __do_fault() just with first 31 patches. I
suspect the folio_add_file_rmap_range() missed some PTEs population. Please give
me few days to find the root cause and fix. Sorry for this.
Regards
Yin, Fengwei
>
>>
>> Thanks,
>> Ryan
>>
>>
>>> + }
>>> +
>>> + if (first)
>>> + nr++;
>>> + } while (page++, --nr_pages > 0);
>>> } else if (folio_test_pmd_mappable(folio)) {
>>> /* That test is redundant: it's for safety or to optimize out */
>>>
>>> @@ -1354,6 +1362,30 @@ void page_add_file_rmap(struct page *page, struct vm_area_struct *vma,
>>> mlock_vma_folio(folio, vma, compound);
>>> }
>>>
>>> +/**
>>> + * page_add_file_rmap - add pte mapping to a file page
>>> + * @page: the page to add the mapping to
>>> + * @vma: the vm area in which the mapping is added
>>> + * @compound: charge the page as compound or small page
>>> + *
>>> + * The caller needs to hold the pte lock.
>>> + */
>>> +void page_add_file_rmap(struct page *page, struct vm_area_struct *vma,
>>> + bool compound)
>>> +{
>>> + struct folio *folio = page_folio(page);
>>> + unsigned int nr_pages;
>>> +
>>> + VM_WARN_ON_ONCE_PAGE(compound && !PageTransHuge(page), page);
>>> +
>>> + if (likely(!compound))
>>> + nr_pages = 1;
>>> + else
>>> + nr_pages = folio_nr_pages(folio);
>>> +
>>> + folio_add_file_rmap_range(folio, page, nr_pages, vma, compound);
>>> +}
>>> +
>>> /**
>>> * page_remove_rmap - take down pte mapping from a page
>>> * @page: page to remove mapping from
>>
>
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