lkml.org 
[lkml]   [2024]   [Apr]   [9]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
SubjectRe: [PATCH 10/10] mm: page_alloc: consolidate free page accounting
From


On 2024/4/9 14:23, Vlastimil Babka wrote:
> On 4/8/24 4:23 PM, Johannes Weiner wrote:
>> On Mon, Apr 08, 2024 at 09:38:20AM +0200, Vlastimil Babka wrote:
>>> On 4/7/24 12:19 PM, Baolin Wang wrote:
>>>> On 2024/3/21 02:02, Johannes Weiner wrote:
>>>>>
>>>>> + account_freepages(page, zone, 1 << order, migratetype);
>>>>> +
>>>>> while (order < MAX_PAGE_ORDER) {
>>>>> - if (compaction_capture(capc, page, order, migratetype)) {
>>>>> - __mod_zone_freepage_state(zone, -(1 << order),
>>>>> - migratetype);
>>>>> + int buddy_mt = migratetype;
>>>>> +
>>>>> + if (compaction_capture(capc, page, order, migratetype))
>>>>> return;
>>>>> - }
>>>>
>>>> IIUC, if the released page is captured by compaction, then the
>>>> statistics for free pages should be correspondingly decreased,
>>>> otherwise, there will be a slight regression for my thpcompact benchmark.
>>>>
>>>> thpcompact Percentage Faults Huge
>>>> k6.9-rc2-base base + patch10 + 2 fixes
>>>> Percentage huge-1 78.18 ( 0.00%) 71.92 ( -8.01%)
>>>> Percentage huge-3 86.70 ( 0.00%) 86.07 ( -0.73%)
>>>> Percentage huge-5 90.26 ( 0.00%) 78.02 ( -13.57%)
>>>> Percentage huge-7 92.34 ( 0.00%) 78.67 ( -14.81%)
>>>> Percentage huge-12 91.18 ( 0.00%) 81.04 ( -11.12%)
>>>> Percentage huge-18 89.00 ( 0.00%) 79.57 ( -10.60%)
>>>> Percentage huge-24 90.52 ( 0.00%) 80.07 ( -11.54%)
>>>> Percentage huge-30 94.44 ( 0.00%) 96.28 ( 1.95%)
>>>> Percentage huge-32 93.09 ( 0.00%) 99.39 ( 6.77%)
>>>>
>>>> I add below fix based on your fix 2, then the thpcompact Percentage
>>>> looks good. How do you think for the fix?
>>>
>>> Yeah another well spotted, thanks. "slight regression" is an understatement,
>>> this affects not just a "statistics" but very important counter
>>> NR_FREE_PAGES which IIUC would eventually become larger than reality, make
>>> the watermark checks false positive and result in depleted reserves etc etc.
>>> Actually wondering why we're not seeing -next failures already (or maybe I
>>> just haven't noticed).
>>
>> Good catch indeed.
>>
>> Trying to understand why I didn't notice this during testing, and I
>> think it's because I had order-10 pageblocks in my config. There is
>> this in compaction_capture():
>>
>> if (order < pageblock_order && migratetype == MIGRATE_MOVABLE)
>> return false;
>>
>> Most compaction is for order-9 THPs on movable blocks, so I didn't get
>> much capturing in practice in order for that leak to be noticable.
>>
>> In earlier versions of the patches I had more aggressive capturing,
>> but also did the accounting in add_page_to/del_page_from_freelist(),
>> so capturing only steals what's already accounted to be off list.
>>
>> With the __add/__del and the consolidated account_freepages()
>> optimization, compaction_capture() needs explicit accounting again.
>>
>>>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>>>> index 8330c5c2de6b..2facf844ef84 100644
>>>> --- a/mm/page_alloc.c
>>>> +++ b/mm/page_alloc.c
>>>> @@ -805,8 +805,10 @@ static inline void __free_one_page(struct page *page,
>>>> while (order < MAX_PAGE_ORDER) {
>>>> int buddy_mt = migratetype;
>>>>
>>>> - if (compaction_capture(capc, page, order, migratetype))
>>>> + if (compaction_capture(capc, page, order, migratetype)) {
>>>> + account_freepages(zone, -(1 << order), migratetype);
>>>> return;
>>>> + }
>>>>
>>>> buddy = find_buddy_page_pfn(page, pfn, order, &buddy_pfn);
>>>> if (!buddy)
>>>>
>>>> With my fix, the THP percentage looks better:
>>>> k6.9-rc2-base base + patch10 + 2 fixes +
>>>> my fix
>>>> Percentage huge-1 78.18 ( 0.00%) 82.83 ( 5.94%)
>>>> Percentage huge-3 86.70 ( 0.00%) 93.47 ( 7.81%)
>>>> Percentage huge-5 90.26 ( 0.00%) 94.73 ( 4.95%)
>>>> Percentage huge-7 92.34 ( 0.00%) 95.22 ( 3.12%)
>>>> Percentage huge-12 91.18 ( 0.00%) 92.40 ( 1.34%)
>>>> Percentage huge-18 89.00 ( 0.00%) 85.39 ( -4.06%)
>>>> Percentage huge-24 90.52 ( 0.00%) 94.70 ( 4.61%)
>>>> Percentage huge-30 94.44 ( 0.00%) 97.00 ( 2.71%)
>>>> Percentage huge-32 93.09 ( 0.00%) 92.87 ( -0.24%)
>>
>> Acked-by: Johannes Weiner <hannes@cmpxchg.org>
>
> Acked-by: Vlastimil Babka <vbabka@suse.cz>

Thanks.

>> With fixed indentation:
>
> Maybe Baolin could resend the finalized 2 fixups in a more ready-to-pick form?

Sure, I've send it out.

And I see Andrew has already folded the first fix
("mm-page_alloc-fix-freelist-movement-during-block-conversion-fix") into
the patch set. If a formal fix patch is needed, Andrew, please let me know.

\
 
 \ /
  Last update: 2024-05-27 16:30    [W:0.090 / U:0.536 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site