On 07/08/2020 05:31 AM, John Hubbard wrote: > On 2020-07-06 17:06, Anshuman Khandual wrote: >> Add following new vmstat events which will help in validating THP migration >> without split. Statistics reported through these new VM events will help in >> performance debugging. >> >> 1. THP_MIGRATION_SUCCESS >> 2. THP_MIGRATION_FAILURE >> 3. THP_MIGRATION_SPLIT >> >> In addition, these new events also update normal page migration statistics >> appropriately via PGMIGRATE_SUCCESS and PGMIGRATE_FAILURE. While here, this >> updates current trace event 'mm_migrate_pages' to accommodate now available >> THP statistics. >> >> Cc: Daniel Jordan <daniel.m.jordan@xxxxxxxxxx> >> Cc: Hugh Dickins <hughd@xxxxxxxxxx> >> Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx> >> Cc: Zi Yan <ziy@xxxxxxxxxx> >> Cc: John Hubbard <jhubbard@xxxxxxxxxx> >> Cc: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx> >> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> >> Cc: linux-mm@xxxxxxxxx >> Cc: linux-kernel@xxxxxxxxxxxxxxx >> Signed-off-by: Zi Yan <ziy@xxxxxxxxxx> >> Signed-off-by: Anshuman Khandual <anshuman.khandual@xxxxxxx> > > > This is missing the Documentation/ Cc's, did you run scripts/get_maintainer.pl? I'm > adding linux-doc and Jonathan Corbet, for now at least. And I'll refrain from > trimming the reply. I had missed the Documention/ Cc's, thanks for adding them here. Will update the Cc list next time around. > > >> --- >> Changes in V3: >> >> - Formatted new events documentation with 'fmt' tool per Matthew >> - Made events universally available i.e dropped ARCH_ENABLE_THP_MIGRATION >> - Added THP_MIGRATION_SPLIT >> - Updated trace_mm_migrate_pages() with THP events >> - Made THP events update normal page migration events as well >> >> Changes in V2: (https://patchwork.kernel.org/patch/11586893/) >> >> - Dropped PMD reference both from code and commit message per Matthew >> - Added documentation and updated the commit message per Daniel >> >> Changes in V1: (https://patchwork.kernel.org/patch/11564497/) >> >> - Changed function name as thp_pmd_migration_success() per John >> - Folded in a fix (https://patchwork.kernel.org/patch/11563009/) from Hugh >> >> Changes in RFC V2: (https://patchwork.kernel.org/patch/11554861/) >> >> - Decopupled and renamed VM events from their implementation per Zi and John >> - Added THP_PMD_MIGRATION_FAILURE VM event upon allocation failure and split >> >> Changes in RFC V1: (https://patchwork.kernel.org/patch/11542055/) >> >> Documentation/vm/page_migration.rst | 19 +++++++++++ >> include/linux/vm_event_item.h | 3 ++ >> include/trace/events/migrate.h | 17 ++++++++-- >> mm/migrate.c | 49 ++++++++++++++++++++++++++--- >> mm/vmstat.c | 3 ++ >> 5 files changed, 84 insertions(+), 7 deletions(-) >> >> diff --git a/Documentation/vm/page_migration.rst b/Documentation/vm/page_migration.rst >> index 1d6cd7db4e43..e65d49f3cf86 100644 >> --- a/Documentation/vm/page_migration.rst >> +++ b/Documentation/vm/page_migration.rst >> @@ -253,5 +253,24 @@ which are function pointers of struct address_space_operations. >> PG_isolated is alias with PG_reclaim flag so driver shouldn't use the flag >> for own purpose. >> +Quantifying Migration >> +===================== >> +Following events can be used to quantify page migration. >> + >> +1. PGMIGRATE_SUCCESS /* Normal page migration success */ > > > This doesn't explain what's going on with the new combined counter > behavior. See the proposal below. > > >> +2. PGMIGRATE_FAIL /* Normal page migration failure */ >> +3. THP_MIGRATION_SUCCESS /* Transparent huge page migration success */ >> +4. THP_MIGRATION_FAILURE /* Transparent huge page migration failure */ > > > Shouldn't that be THP_MIGRATION_FAIL, in order to match the existing naming > scheme here? Sure, will change it. > > >> +5. THP_MIGRATION_SPLIT /* Transparent huge page got split, retried */ >> + >> +THP_MIGRATION_SUCCESS is when THP is migrated successfully without getting >> +split into it's subpages. THP_MIGRATION_FAILURE is when THP could neither >> +be migrated nor be split. THP_MIGRATION_SPLIT is when THP could not >> +just be migrated as is but instead get split into it's subpages and later >> +retried as normal pages. THP events would also update normal page migration >> +statistics PGMIGRATE_SUCCESS and PGMIGRATE_FAILURE. These events will help >> +in quantifying and analyzing various THP migration events including both >> +success and failure cases. >> + > > > I would like to propose the following instead of the above. It's rewritten > so as to add explanations for the new behavior, remove the redundancy (the last > sentence in particular is a justification, and belongs in a commit log if anywhere, > not in the doc itself), fix a few typos, use the full 80 columns, and clarify a > bit as well. It uses the new THP_MIGRATION_FAIL name: > > > Monitoring Migration > ===================== > > The following events (counters) can be used to monitor page migration. > > 1. PGMIGRATE_SUCCESS: Normal page migration success. Each count means that a > page was migrated. If the page was a non-THP page, then this counter is > increased by one. If the page was a THP, then this counter is increased by > the number of THP subpages. For example, migration of a single 2MB THP that > has 4KB-size base pages (subpages) will cause this counter to increase by > 512. > > 2. PGMIGRATE_FAIL: Normal page migration failure. Same counting rules as for > _SUCCESS, above: this will be increased by the number of subpages, if it was > a THP. > > 3. THP_MIGRATION_SUCCESS: A THP was migrated without being split. > > 4. THP_MIGRATION_FAIL: A THP could not be migrated at all, even after being > split. > > 5. THP_MIGRATION_SPLIT: A THP was migrated, but not as such: first, the THP had > to be split. After splitting, a migration retry was used for the sub-pages, > and that retry succeeded. The last part might not be true. All that THP_MIGRATION_SPLIT tracks is whether the THP was split or not. Whether it's subpages got successfully migrated later or not, would be hidden in overall PGMIGRATE_SUCCESS and PGMIGRATE_FAIL values. > > THP_MIGRATION_* events also update the appropriate PGMIGRATE_SUCCESS or > PGMIGRATE_FAILURE events. For example, a THP migration failure will cause both > THP_MIGRATION_FAIL and PGMIGRATE_FAIL to increase. Above explanation (probably with some changes) looks better, will update. > > >> Christoph Lameter, May 8, 2006. >> Minchan Kim, Mar 28, 2016. >> diff --git a/include/linux/vm_event_item.h b/include/linux/vm_event_item.h >> index 24fc7c3ae7d6..5e7ffa025589 100644 >> --- a/include/linux/vm_event_item.h >> +++ b/include/linux/vm_event_item.h >> @@ -95,6 +95,9 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT, >> THP_ZERO_PAGE_ALLOC_FAILED, >> THP_SWPOUT, >> THP_SWPOUT_FALLBACK, >> + THP_MIGRATION_SUCCESS, >> + THP_MIGRATION_FAILURE, >> + THP_MIGRATION_SPLIT, >> #endif >> #ifdef CONFIG_MEMORY_BALLOON >> BALLOON_INFLATE, >> diff --git a/include/trace/events/migrate.h b/include/trace/events/migrate.h >> index 705b33d1e395..4d434398d64d 100644 >> --- a/include/trace/events/migrate.h >> +++ b/include/trace/events/migrate.h >> @@ -46,13 +46,18 @@ MIGRATE_REASON >> TRACE_EVENT(mm_migrate_pages, >> TP_PROTO(unsigned long succeeded, unsigned long failed, >> - enum migrate_mode mode, int reason), >> + unsigned long thp_succeeded, unsigned long thp_failed, >> + unsigned long thp_split, enum migrate_mode mode, int reason), >> - TP_ARGS(succeeded, failed, mode, reason), >> + TP_ARGS(succeeded, failed, thp_succeeded, thp_failed, >> + thp_split, mode, reason), >> TP_STRUCT__entry( >> __field( unsigned long, succeeded) >> __field( unsigned long, failed) >> + __field( unsigned long, thp_succeeded) >> + __field( unsigned long, thp_failed) >> + __field( unsigned long, thp_split) >> __field( enum migrate_mode, mode) >> __field( int, reason) >> ), >> @@ -60,13 +65,19 @@ TRACE_EVENT(mm_migrate_pages, >> TP_fast_assign( >> __entry->succeeded = succeeded; >> __entry->failed = failed; >> + __entry->thp_succeeded = thp_succeeded; >> + __entry->thp_failed = thp_failed; >> + __entry->thp_split = thp_split; >> __entry->mode = mode; >> __entry->reason = reason; >> ), >> - TP_printk("nr_succeeded=%lu nr_failed=%lu mode=%s reason=%s", >> + TP_printk("nr_succeeded=%lu nr_failed=%lu nr_thp_succeeded=%lu nr_thp_failed=%lu nr_thp_split=%lu mode=%s reason=%s", >> __entry->succeeded, >> __entry->failed, >> + __entry->thp_succeeded, >> + __entry->thp_failed, >> + __entry->thp_split, >> __print_symbolic(__entry->mode, MIGRATE_MODE), >> __print_symbolic(__entry->reason, MIGRATE_REASON)) >> ); >> diff --git a/mm/migrate.c b/mm/migrate.c >> index f37729673558..baf3cc477d11 100644 >> --- a/mm/migrate.c >> +++ b/mm/migrate.c >> @@ -1429,22 +1429,35 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page, >> enum migrate_mode mode, int reason) >> { >> int retry = 1; >> + int thp_retry = 1; >> int nr_failed = 0; >> int nr_succeeded = 0; >> + int nr_thp_succeeded = 0; >> + int nr_thp_failed = 0; >> + int nr_thp_split = 0; >> int pass = 0; >> + bool is_thp = false; >> struct page *page; >> struct page *page2; >> int swapwrite = current->flags & PF_SWAPWRITE; >> - int rc; >> + int rc, thp_nr_pages; >> if (!swapwrite) >> current->flags |= PF_SWAPWRITE; >> - for(pass = 0; pass < 10 && retry; pass++) { >> + for (pass = 0; pass < 10 && (retry || thp_retry); pass++) { >> retry = 0; >> + thp_retry = 0; >> list_for_each_entry_safe(page, page2, from, lru) { >> retry: >> + /* >> + * THP statistics is based on the source huge page. >> + * Capture required information that might get lost >> + * during migration. >> + */ >> + is_thp = PageTransHuge(page); >> + thp_nr_pages = hpage_nr_pages(page); >> cond_resched(); >> if (PageHuge(page)) >> @@ -1475,15 +1488,30 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page, >> unlock_page(page); >> if (!rc) { >> list_safe_reset_next(page, page2, lru); >> + nr_thp_split++; >> goto retry; >> } >> } >> + if (is_thp) { >> + nr_thp_failed++; >> + nr_failed += thp_nr_pages; >> + goto out; >> + } >> nr_failed++; >> goto out; >> case -EAGAIN: >> + if (is_thp) { >> + thp_retry++; >> + break; >> + } >> retry++; >> break; >> case MIGRATEPAGE_SUCCESS: >> + if (is_thp) { >> + nr_thp_succeeded++; >> + nr_succeeded += thp_nr_pages; >> + break; >> + } >> nr_succeeded++; >> break; >> default: >> @@ -1493,19 +1521,32 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page, >> * removed from migration page list and not >> * retried in the next outer loop. >> */ >> + if (is_thp) { >> + nr_thp_failed++; >> + nr_failed += thp_nr_pages; >> + break; >> + } >> nr_failed++; >> break; >> } >> } >> } >> - nr_failed += retry; >> + nr_failed += retry + thp_retry; >> + nr_thp_failed += thp_retry; >> rc = nr_failed; >> out: >> if (nr_succeeded) >> count_vm_events(PGMIGRATE_SUCCESS, nr_succeeded); >> if (nr_failed) >> count_vm_events(PGMIGRATE_FAIL, nr_failed); >> - trace_mm_migrate_pages(nr_succeeded, nr_failed, mode, reason); >> + if (nr_thp_succeeded) >> + count_vm_events(THP_MIGRATION_SUCCESS, nr_thp_succeeded); >> + if (nr_thp_failed) >> + count_vm_events(THP_MIGRATION_FAILURE, nr_thp_failed); >> + if (nr_thp_split) >> + count_vm_events(THP_MIGRATION_SPLIT, nr_thp_split); > > As mentioned in the other thread, those "ifs" should be removed. I think you > can also get away with removing the two pre-existing "ifs" in the same > patch, too, just to keep the whole set consistent and more readable. Makes sense, will do.
