On 09.08.24 09:04, Barry Song wrote:
I would appreciate if we leave the rmap out here.
Can't we handle that when actually freeing the folio? folio_test_anon()
is sticky until freed.
To be clearer: we increment the counter when we set a folio anon, which
should indeed only happen in folio_add_new_anon_rmap(). We'll have to
ignore hugetlb here where we do it in hugetlb_add_new_anon_rmap().
Then, when we free an anon folio we decrement the counter. (hugetlb
should clear the anon flag when an anon folio gets freed back to its
allocator -- likely that is already done).
Sorry that I am talking to myself: I'm wondering if we also have to
adjust the counter when splitting a large folio to multiple
smaller-but-still-large folios.
Hi David,
The conceptual code is shown below. Does this make more
sense to you? we have a line "mod_mthp_stat(new_order,
MTHP_STAT_NR_ANON, 1 << (order - new_order));"
@@ -3270,8 +3272,9 @@ int split_huge_page_to_list_to_order(struct page *page, struct list_head *list,
struct deferred_split *ds_queue = get_deferred_split_queue(folio);
/* reset xarray order to new order after split */
XA_STATE_ORDER(xas, &folio->mapping->i_pages, folio->index, new_order);
- struct anon_vma *anon_vma = NULL;
+ bool is_anon = folio_test_anon(folio);
struct address_space *mapping = NULL;
+ struct anon_vma *anon_vma = NULL;
int order = folio_order(folio);
int extra_pins, ret;
pgoff_t end;
@@ -3283,7 +3286,7 @@ int split_huge_page_to_list_to_order(struct page *page, struct list_head *list,
if (new_order >= folio_order(folio))
return -EINVAL;
- if (folio_test_anon(folio)) {
+ if (is_anon) {
/* order-1 is not supported for anonymous THP. */
if (new_order == 1) {
VM_WARN_ONCE(1, "Cannot split to order-1 folio");
@@ -3323,7 +3326,7 @@ int split_huge_page_to_list_to_order(struct page *page, struct list_head *list,
if (folio_test_writeback(folio))
return -EBUSY;
- if (folio_test_anon(folio)) {
+ if (is_anon) {
/*
* The caller does not necessarily hold an mmap_lock that would
* prevent the anon_vma disappearing so we first we take a
@@ -3437,6 +3440,10 @@ int split_huge_page_to_list_to_order(struct page *page, struct list_head *list,
}
}
+ if (is_anon) {
+ mod_mthp_stat(order, MTHP_STAT_NR_ANON, -1);
+ mod_mthp_stat(new_order, MTHP_STAT_NR_ANON, 1 << (order - new_order));
+ }
__split_huge_page(page, list, end, new_order);
ret = 0;
} else {
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 408ef3d25cf5..c869d0601614 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1039,6 +1039,7 @@ __always_inline bool free_pages_prepare(struct page *page,
bool skip_kasan_poison = should_skip_kasan_poison(page);
bool init = want_init_on_free();
bool compound = PageCompound(page);
+ bool anon = PageAnon(page);
VM_BUG_ON_PAGE(PageTail(page), page);
@@ -1130,6 +1131,9 @@ __always_inline bool free_pages_prepare(struct page *page,
debug_pagealloc_unmap_pages(page, 1 << order);
+ if (anon && compound)
+ mod_mthp_stat(order, MTHP_STAT_NR_ANON, -1);
+
return true;
I'd have placed it here, when we are already passed the "PageMappingFlags" check and
shouldn't have any added overhead for most !anon pages IIRC (mostly only anon/ksm pages should
run into that path).
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 408ef3d25cf5..a11b9dd62964 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1079,8 +1079,11 @@ __always_inline bool free_pages_prepare(struct page *page,
(page + i)->flags &= ~PAGE_FLAGS_CHECK_AT_PREP;
}
}
- if (PageMappingFlags(page))
+ if (PageMappingFlags(page)) {
+ if (PageAnon(page) && compound)
+ mod_mthp_stat(order, MTHP_STAT_NR_ANON, -1);
page->mapping = NULL;
+ }
if (is_check_pages_enabled()) {
if (free_page_is_bad(page))
bad++;
Conceptually LGTM. We account an anon folio as long as it's anon,
even when still GUP-pinned after unmapping it or when temporarily
unmapping+remapping it during migration.
--
Cheers,
David / dhildenb
