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mm: migrate: fix the return value of migrate_pages() 

Patch series "Improve the migration stats".

According to talk with Zi Yan [1], this patch set changes the return
value of migrate_pages() to avoid returning a number which is larger
than the number of pages the users tried to migrate by move_pages()
syscall.  Also fix the hugetlb migration stats and migration stats in
trace_mm_compaction_migratepages().

[1] https://lore.kernel.org/linux-mm/7E44019D-2A5D-4BA7-B4D5-00D4712F1687@nvidia.com/

This patch (of 3):

As Zi Yan pointed out, the syscall move_pages() can return a
non-migrated number larger than the number of pages the users tried to
migrate, when a THP page is failed to migrate.  This is confusing for
users.

Since other migration scenarios do not care about the actual
non-migrated number of pages except the memory compaction migration
which will fix in following patch.  Thus we can change the return value
to return the number of {normal page, THP, hugetlb} instead to avoid
this issue, and the number of THP splits will be considered as the
number of non-migrated THP, no matter how many subpages of the THP are
migrated successfully.  Meanwhile we should still keep the migration
counters using the number of normal pages.

Link: https://lkml.kernel.org/r/cover.1636275127.git.baolin.wang@linux.alibaba.com
Link: https://lkml.kernel.org/r/6486fabc3e8c66ff613e150af25e89b3147977a6.1636275127.git.baolin.wang@linux.alibaba.com
Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Signed-off-by: Zi Yan <ziy@nvidia.com>
Co-developed-by: Zi Yan <ziy@nvidia.com>
Cc: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Baolin Wang 2022-01-14 14:08:34 -08:00 committed by Linus Torvalds
parent d6aba4c8e2
commit b5bade978e
1 changed files with 47 additions and 16 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

63
mm/migrate.c
View File

@ -1421,7 +1421,7 @@ static inline int try_split_thp(struct page *page, struct page **page2,
* @mode: The migration mode that specifies the constraints for
* page migration, if any.
* @reason: The reason for page migration.
* @ret_succeeded: Set to the number of pages migrated successfully if
* @ret_succeeded: Set to the number of normal pages migrated successfully if
* the caller passes a non-NULL pointer.
*
* The function returns after 10 attempts or if no pages are movable any more
@ -1429,7 +1429,9 @@ static inline int try_split_thp(struct page *page, struct page **page2,
* It is caller's responsibility to call putback_movable_pages() to return pages
* to the LRU or free list only if ret != 0.
*
* Returns the number of pages that were not migrated, or an error code.
* Returns the number of {normal page, THP} that were not migrated, or an error code.
* The number of THP splits will be considered as the number of non-migrated THP,
* no matter how many subpages of the THP are migrated successfully.
*/
int migrate_pages(struct list_head *from, new_page_t get_new_page,
free_page_t put_new_page, unsigned long private,
@ -1438,6 +1440,7 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
int retry = 1;
int thp_retry = 1;
int nr_failed = 0;
int nr_failed_pages = 0;
int nr_succeeded = 0;
int nr_thp_succeeded = 0;
int nr_thp_failed = 0;
@ -1449,13 +1452,16 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
int swapwrite = current->flags & PF_SWAPWRITE;
int rc, nr_subpages;
LIST_HEAD(ret_pages);
LIST_HEAD(thp_split_pages);
bool nosplit = (reason == MR_NUMA_MISPLACED);
bool no_subpage_counting = false;
trace_mm_migrate_pages_start(mode, reason);
if (!swapwrite)
current->flags |= PF_SWAPWRITE;
thp_subpage_migration:
for (pass = 0; pass < 10 && (retry || thp_retry); pass++) {
retry = 0;
thp_retry = 0;
@ -1504,18 +1510,20 @@ retry:
case -ENOSYS:
/* THP migration is unsupported */
if (is_thp) {
if (!try_split_thp(page, &page2, from)) {
nr_thp_failed++;
if (!try_split_thp(page, &page2, &thp_split_pages)) {
nr_thp_split++;
goto retry;
}
nr_thp_failed++;
nr_failed += nr_subpages;
nr_failed_pages += nr_subpages;
break;
}
/* Hugetlb migration is unsupported */
nr_failed++;
if (!no_subpage_counting)
nr_failed++;
nr_failed_pages++;
break;
case -ENOMEM:
/*
@ -1524,16 +1532,19 @@ retry:
* THP NUMA faulting doesn't split THP to retry.
*/
if (is_thp && !nosplit) {
if (!try_split_thp(page, &page2, from)) {
nr_thp_failed++;
if (!try_split_thp(page, &page2, &thp_split_pages)) {
nr_thp_split++;
goto retry;
}
nr_thp_failed++;
nr_failed += nr_subpages;
nr_failed_pages += nr_subpages;
goto out;
}
nr_failed++;
if (!no_subpage_counting)
nr_failed++;
nr_failed_pages++;
goto out;
case -EAGAIN:
if (is_thp) {
@ -1559,17 +1570,37 @@ retry:
*/
if (is_thp) {
nr_thp_failed++;
nr_failed += nr_subpages;
nr_failed_pages += nr_subpages;
break;
}
nr_failed++;
if (!no_subpage_counting)
nr_failed++;
nr_failed_pages++;
break;
}
}
}
nr_failed += retry + thp_retry;
nr_failed += retry;
nr_thp_failed += thp_retry;
rc = nr_failed;
/*
* Try to migrate subpages of fail-to-migrate THPs, no nr_failed
* counting in this round, since all subpages of a THP is counted
* as 1 failure in the first round.
*/
if (!list_empty(&thp_split_pages)) {
/*
* Move non-migrated pages (after 10 retries) to ret_pages
* to avoid migrating them again.
*/
list_splice_init(from, &ret_pages);
list_splice_init(&thp_split_pages, from);
no_subpage_counting = true;
retry = 1;
goto thp_subpage_migration;
}
rc = nr_failed + nr_thp_failed;
out:
/*
* Put the permanent failure page back to migration list, they
@ -1578,11 +1609,11 @@ out:
list_splice(&ret_pages, from);
count_vm_events(PGMIGRATE_SUCCESS, nr_succeeded);
count_vm_events(PGMIGRATE_FAIL, nr_failed);
count_vm_events(PGMIGRATE_FAIL, nr_failed_pages);
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,
trace_mm_migrate_pages(nr_succeeded, nr_failed_pages, nr_thp_succeeded,
nr_thp_failed, nr_thp_split, mode, reason);
if (!swapwrite)