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@xxxxxxxxxxx>
With fixed indentation:
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 70f82635f650..96815e3c22f2 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)
