Messages in this thread | | | Subject | Re: [RFC] mm/vmstat: Add events for THP migration without split | From | John Hubbard <> | Date | Thu, 14 May 2020 11:29:23 -0700 |
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On 2020-05-11 21:22, Anshuman Khandual wrote: > Add the following new trace events which will help in validating migration > events involving PMD based THP pages. > > 1. THP_PMD_MIGRATION_ENTRY_SET > 2. THP_PMD_MIGRATION_ENTRY_REMOVE > > There are no clear method to confirm whether a THP migration happened with > out involving it's split. These trace events along with PGMIGRATE_SUCCESS > and PGMIGRATE_FAILURE will provide additional insights. After this change, >
Hi Anshuman,
It's very nice to see this work, and I think that reporting a bit more about THP migration stats is going to make development and performance debugging a lot more efficient (and pleasant).
> A single 2M THP (2K base page) when migrated > > 1. Without split > > ................ > pgmigrate_success 1 > pgmigrate_fail 0 > ................ > thp_pmd_migration_entry_set 1 > thp_pmd_migration_entry_remove 1 > ................ >
I do think we should decouple the trace event name(s) just a *little* more, from the mechanisms used to migrate THPs. In other words, let's report the number of THP migration successes, and name it accordingly--rather than "set" and "remove", which are pretty low-level and furthermore depend on today's exact code.
Maybe Zi Yan's recommended name is exactly right, in fact:
THP_PMD_MIGRATION_SUCCESS
thanks, -- John Hubbard NVIDIA
> 2. With split > > ................ > pgmigrate_success 512 > pgmigrate_fail 0 > ................ > thp_pmd_migration_entry_set 0 > thp_pmd_migration_entry_remove 0 > ................ > > pgmigrate_success as 1 instead of 512, provides a hint for possible THP > migration event. But then it gets mixed with normal page migrations over > time. These additional trace events provide required co-relation. > > Cc: Andrew Morton <akpm@linux-foundation.org> > Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> > Cc: Zi Yan <ziy@nvidia.com> > Cc: linux-mm@kvack.org > Cc: linux-kernel@vger.kernel.org > Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com> > --- > This is an indirect way for counting PMD migrations without split. Is there > a better method possible ? Just request for comments at the moment. > > include/linux/vm_event_item.h | 4 ++++ > mm/migrate.c | 1 + > mm/rmap.c | 1 + > mm/vmstat.c | 4 ++++ > 4 files changed, 10 insertions(+) > > diff --git a/include/linux/vm_event_item.h b/include/linux/vm_event_item.h > index ffef0f279747..4b25102cf3ad 100644 > --- a/include/linux/vm_event_item.h > +++ b/include/linux/vm_event_item.h > @@ -91,6 +91,10 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT, > THP_ZERO_PAGE_ALLOC_FAILED, > THP_SWPOUT, > THP_SWPOUT_FALLBACK, > +#ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION > + THP_PMD_MIGRATION_ENTRY_SET, > + THP_PMD_MIGRATION_ENTRY_REMOVE, > +#endif > #endif > #ifdef CONFIG_MEMORY_BALLOON > BALLOON_INFLATE, > diff --git a/mm/migrate.c b/mm/migrate.c > index 7160c1556f79..8d50d55cbe97 100644 > --- a/mm/migrate.c > +++ b/mm/migrate.c > @@ -228,6 +228,7 @@ static bool remove_migration_pte(struct page *page, struct vm_area_struct *vma, > if (!pvmw.pte) { > VM_BUG_ON_PAGE(PageHuge(page) || !PageTransCompound(page), page); > remove_migration_pmd(&pvmw, new); > + count_vm_event(THP_PMD_MIGRATION_ENTRY_REMOVE); > continue; > } > #endif > diff --git a/mm/rmap.c b/mm/rmap.c > index f79a206b271a..3c1fe3f45cb5 100644 > --- a/mm/rmap.c > +++ b/mm/rmap.c > @@ -1418,6 +1418,7 @@ static bool try_to_unmap_one(struct page *page, struct vm_area_struct *vma, > VM_BUG_ON_PAGE(PageHuge(page) || !PageTransCompound(page), page); > > set_pmd_migration_entry(&pvmw, page); > + count_vm_event(THP_PMD_MIGRATION_ENTRY_SET); > continue; > } > #endif > diff --git a/mm/vmstat.c b/mm/vmstat.c > index 96d21a792b57..a5254b7ee531 100644 > --- a/mm/vmstat.c > +++ b/mm/vmstat.c > @@ -1274,6 +1274,10 @@ const char * const vmstat_text[] = { > "thp_zero_page_alloc_failed", > "thp_swpout", > "thp_swpout_fallback", > +#ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION > + "thp_pmd_migration_entry_set", > + "thp_pmd_migration_entry_remove", > +#endif > #endif > #ifdef CONFIG_MEMORY_BALLOON > "balloon_inflate", >
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