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migrate: convert __unmap_and_move() to use folios

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Removes a lot of calls to compound_head().  Also remove a VM_BUG_ON that
can never trigger as the PageAnon bit is the bottom bit of page->mapping.

Link: https://lkml.kernel.org/r/20220902194653.1739778-51-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Matthew Wilcox (Oracle) 2022-09-02 20:46:46 +01:00 committed by Andrew Morton
parent 595af4c936
commit 682a71a1b6
1 changed files with 37 additions and 38 deletions
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75
mm/migrate.c
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@ -993,17 +993,15 @@ out:
return rc;
}
static int __unmap_and_move(struct page *page, struct page *newpage,
static int __unmap_and_move(struct folio *src, struct folio *dst,
int force, enum migrate_mode mode)
{
struct folio *folio = page_folio(page);
struct folio *dst = page_folio(newpage);
int rc = -EAGAIN;
bool page_was_mapped = false;
struct anon_vma *anon_vma = NULL;
bool is_lru = !__PageMovable(page);
bool is_lru = !__PageMovable(&src->page);
if (!trylock_page(page)) {
if (!folio_trylock(src)) {
if (!force || mode == MIGRATE_ASYNC)
goto out;
@ -1023,10 +1021,10 @@ static int __unmap_and_move(struct page *page, struct page *newpage,
if (current->flags & PF_MEMALLOC)
goto out;
lock_page(page);
folio_lock(src);
}
if (PageWriteback(page)) {
if (folio_test_writeback(src)) {
/*
* Only in the case of a full synchronous migration is it
* necessary to wait for PageWriteback. In the async case,
@ -1043,12 +1041,12 @@ static int __unmap_and_move(struct page *page, struct page *newpage,
}
if (!force)
goto out_unlock;
wait_on_page_writeback(page);
folio_wait_writeback(src);
}
/*
* By try_to_migrate(), page->mapcount goes down to 0 here. In this case,
* we cannot notice that anon_vma is freed while we migrates a page.
* By try_to_migrate(), src->mapcount goes down to 0 here. In this case,
* we cannot notice that anon_vma is freed while we migrate a page.
* This get_anon_vma() delays freeing anon_vma pointer until the end
* of migration. File cache pages are no problem because of page_lock()
* File Caches may use write_page() or lock_page() in migration, then,
@ -1060,22 +1058,22 @@ static int __unmap_and_move(struct page *page, struct page *newpage,
* because that implies that the anon page is no longer mapped
* (and cannot be remapped so long as we hold the page lock).
*/
if (PageAnon(page) && !PageKsm(page))
anon_vma = page_get_anon_vma(page);
if (folio_test_anon(src) && !folio_test_ksm(src))
anon_vma = page_get_anon_vma(&src->page);
/*
* Block others from accessing the new page when we get around to
* establishing additional references. We are usually the only one
* holding a reference to newpage at this point. We used to have a BUG
* here if trylock_page(newpage) fails, but would like to allow for
* cases where there might be a race with the previous use of newpage.
* holding a reference to dst at this point. We used to have a BUG
* here if folio_trylock(dst) fails, but would like to allow for
* cases where there might be a race with the previous use of dst.
* This is much like races on refcount of oldpage: just don't BUG().
*/
if (unlikely(!trylock_page(newpage)))
if (unlikely(!folio_trylock(dst)))
goto out_unlock;
if (unlikely(!is_lru)) {
rc = move_to_new_folio(dst, folio, mode);
rc = move_to_new_folio(dst, src, mode);
goto out_unlock_both;
}
@ -1083,7 +1081,7 @@ static int __unmap_and_move(struct page *page, struct page *newpage,
* Corner case handling:
* 1. When a new swap-cache page is read into, it is added to the LRU
* and treated as swapcache but it has no rmap yet.
* Calling try_to_unmap() against a page->mapping==NULL page will
* Calling try_to_unmap() against a src->mapping==NULL page will
* trigger a BUG. So handle it here.
* 2. An orphaned page (see truncate_cleanup_page) might have
* fs-private metadata. The page can be picked up due to memory
@ -1091,57 +1089,56 @@ static int __unmap_and_move(struct page *page, struct page *newpage,
* invisible to the vm, so the page can not be migrated. So try to
* free the metadata, so the page can be freed.
*/
if (!page->mapping) {
VM_BUG_ON_PAGE(PageAnon(page), page);
if (page_has_private(page)) {
try_to_free_buffers(folio);
if (!src->mapping) {
if (folio_test_private(src)) {
try_to_free_buffers(src);
goto out_unlock_both;
}
} else if (page_mapped(page)) {
} else if (folio_mapped(src)) {
/* Establish migration ptes */
VM_BUG_ON_PAGE(PageAnon(page) && !PageKsm(page) && !anon_vma,
page);
try_to_migrate(folio, 0);
VM_BUG_ON_FOLIO(folio_test_anon(src) &&
!folio_test_ksm(src) && !anon_vma, src);
try_to_migrate(src, 0);
page_was_mapped = true;
}
if (!page_mapped(page))
rc = move_to_new_folio(dst, folio, mode);
if (!folio_mapped(src))
rc = move_to_new_folio(dst, src, mode);
/*
* When successful, push newpage to LRU immediately: so that if it
* When successful, push dst to LRU immediately: so that if it
* turns out to be an mlocked page, remove_migration_ptes() will
* automatically build up the correct newpage->mlock_count for it.
* automatically build up the correct dst->mlock_count for it.
*
* We would like to do something similar for the old page, when
* unsuccessful, and other cases when a page has been temporarily
* isolated from the unevictable LRU: but this case is the easiest.
*/
if (rc == MIGRATEPAGE_SUCCESS) {
lru_cache_add(newpage);
folio_add_lru(dst);
if (page_was_mapped)
lru_add_drain();
}
if (page_was_mapped)
remove_migration_ptes(folio,
rc == MIGRATEPAGE_SUCCESS ? dst : folio, false);
remove_migration_ptes(src,
rc == MIGRATEPAGE_SUCCESS ? dst : src, false);
out_unlock_both:
unlock_page(newpage);
folio_unlock(dst);
out_unlock:
/* Drop an anon_vma reference if we took one */
if (anon_vma)
put_anon_vma(anon_vma);
unlock_page(page);
folio_unlock(src);
out:
/*
* If migration is successful, decrease refcount of the newpage,
* If migration is successful, decrease refcount of dst,
* which will not free the page because new page owner increased
* refcounter.
*/
if (rc == MIGRATEPAGE_SUCCESS)
put_page(newpage);
folio_put(dst);
return rc;
}
@ -1157,6 +1154,7 @@ static int unmap_and_move(new_page_t get_new_page,
enum migrate_reason reason,
struct list_head *ret)
{
struct folio *dst, *src = page_folio(page);
int rc = MIGRATEPAGE_SUCCESS;
struct page *newpage = NULL;
@ -1174,9 +1172,10 @@ static int unmap_and_move(new_page_t get_new_page,
newpage = get_new_page(page, private);
if (!newpage)
return -ENOMEM;
dst = page_folio(newpage);
newpage->private = 0;
rc = __unmap_and_move(page, newpage, force, mode);
rc = __unmap_and_move(src, dst, force, mode);
if (rc == MIGRATEPAGE_SUCCESS)
set_page_owner_migrate_reason(newpage, reason);