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    SubjectRe: [PATCH V4] mm/vmstat: Add events for THP migration without split
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    On 7/9/20 9:34 AM, Zi Yan wrote:
    > On 9 Jul 2020, at 11:34, Randy Dunlap wrote:
    >
    >> Hi,
    >>
    >> I have a few comments on this.
    >>
    >> a. I reported it very early and should have been Cc-ed.
    >>
    >> b. A patch that applies to mmotm or linux-next would have been better
    >> than a full replacement patch.
    >>
    >> c. I tried replacing what I believe is the correct/same patch file in mmotm
    >> and still have build errors.
    >>
    >> (more below)
    >>
    >> On 7/9/20 2:39 AM, Anshuman Khandual wrote:
    >>
    >>> ---
    >>> Applies on 5.8-rc4.
    >>>
    >>> Changes in V4:
    >>>
    >>> - Changed THP_MIGRATION_FAILURE as THP_MIGRATION_FAIL per John
    >>> - Dropped all conditional 'if' blocks in migrate_pages() per Andrew and John
    >>> - Updated migration events documentation per John
    >>> - Updated thp_nr_pages variable as nr_subpages for an expected merge conflict
    >>> - Moved all new THP vmstat events into CONFIG_MIGRATION
    >>> - Updated Cc list with Documentation/ and tracing related addresses
    >>>
    >>> Changes in V3: (https://patchwork.kernel.org/patch/11647237/)
    >>>
    >>> - 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 | 27 +++++++++++++++
    >>> include/linux/vm_event_item.h | 3 ++
    >>> include/trace/events/migrate.h | 17 ++++++++--
    >>> mm/migrate.c | 52 ++++++++++++++++++++++++-----
    >>> mm/vmstat.c | 3 ++
    >>> 5 files changed, 91 insertions(+), 11 deletions(-)
    >>>
    >>
    >>> diff --git a/include/linux/vm_event_item.h b/include/linux/vm_event_item.h
    >>> index 24fc7c3ae7d6..2e6ca53b9bbd 100644
    >>> --- a/include/linux/vm_event_item.h
    >>> +++ b/include/linux/vm_event_item.h
    >>> @@ -56,6 +56,9 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT,
    >>> #endif
    >>> #ifdef CONFIG_MIGRATION
    >>> PGMIGRATE_SUCCESS, PGMIGRATE_FAIL,
    >>> + THP_MIGRATION_SUCCESS,
    >>> + THP_MIGRATION_FAIL,
    >>> + THP_MIGRATION_SPLIT,
    >>
    >> These 3 new symbols are still only present if CONFIG_MIGRATION=y, but the build errors
    >> are using these symbols even when CONFIG_MIGRATION is not set.
    >>
    >>> #endif
    >>> #ifdef CONFIG_COMPACTION
    >>> COMPACTMIGRATE_SCANNED, COMPACTFREE_SCANNED,
    >>
    >>> diff --git a/mm/migrate.c b/mm/migrate.c
    >>> index f37729673558..c706e3576cfc 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, nr_subpages;
    >>>
    >>> 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);
    >>> + nr_subpages = 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 += nr_subpages;
    >>> + 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 += nr_subpages;
    >>> + break;
    >>> + }
    >>> nr_succeeded++;
    >>> break;
    >>> default:
    >>> @@ -1493,19 +1521,27 @@ 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 += nr_subpages;
    >>> + 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);
    >>> + count_vm_events(PGMIGRATE_SUCCESS, nr_succeeded);
    >>> + count_vm_events(PGMIGRATE_FAIL, nr_failed);
    >>> + count_vm_events(THP_MIGRATION_SUCCESS, nr_thp_succeeded);
    >>> + count_vm_events(THP_MIGRATION_FAIL, nr_thp_failed);
    >>> + count_vm_events(THP_MIGRATION_SPLIT, nr_thp_split);
    >>
    >> These references still cause build errors.
    >>
    >>> + trace_mm_migrate_pages(nr_succeeded, nr_failed, nr_thp_succeeded,
    >>> + nr_thp_failed, nr_thp_split, mode, reason);
    >>>
    >>> if (!swapwrite)
    >>> current->flags &= ~PF_SWAPWRITE;
    >>> diff --git a/mm/vmstat.c b/mm/vmstat.c
    >>> index 3fb23a21f6dd..09914a4bfee4 100644
    >>> --- a/mm/vmstat.c
    >>> +++ b/mm/vmstat.c
    >>> @@ -1234,6 +1234,9 @@ const char * const vmstat_text[] = {
    >>> #ifdef CONFIG_MIGRATION
    >>> "pgmigrate_success",
    >>> "pgmigrate_fail",
    >>> + "thp_migration_success",
    >>> + "thp_migration_fail",
    >>> + "thp_migration_split",
    >>> #endif
    >>> #ifdef CONFIG_COMPACTION
    >>> "compact_migrate_scanned",
    >>>
    >>
    >
    > Which arch are you building? I did not see any error
    > after applying this patch on mmotm (reverting the existing ones)
    > and compiling them on x86_64. I used make x86_64_defconfig and
    > unselected COMPACTION and MIGRATION.

    Hi,

    I am trying to build x86_64.
    Maybe I am just having trouble replacing the patch file.
    Like I tried to say, I would prefer to see an incremental patch
    to fix mmotm or linux-next.


    > mm/migrate.c and added vm events will not be used
    > if CONFIG_MIGRATION is unchecked. Why would they cause compilation errors?

    AFAICT, the patch adds these calls:
    + count_vm_events(PGMIGRATE_SUCCESS, nr_succeeded);
    + count_vm_events(PGMIGRATE_FAIL, nr_failed);
    + count_vm_events(THP_MIGRATION_SUCCESS, nr_thp_succeeded);
    + count_vm_events(THP_MIGRATION_FAIL, nr_thp_failed);
    + count_vm_events(THP_MIGRATION_SPLIT, nr_thp_split);
    + trace_mm_migrate_pages(nr_succeeded, nr_failed, nr_thp_succeeded,
    + nr_thp_failed, nr_thp_split, mode, reason);

    even when CONFIG_MIGRATION is not set, but then the THP_MIGRATIION_SUCCESS/FAIL/SPLIT
    symbols are not defined.


    --
    ~Randy

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