@@ -55,18 +55,17 @@ flags the caller provides. The caller is required to pass in a non-null struct
pages* array, and the function then pins pages by incrementing each by a special
value: GUP_PIN_COUNTING_BIAS.
-For compound pages, the GUP_PIN_COUNTING_BIAS scheme is not used. Instead,
-an exact form of pin counting is achieved, by using the 2nd struct page
-in the compound page. A new struct page field, compound_pincount, has
-been added in order to support this.
-
-This approach for compound pages avoids the counting upper limit problems that
-are discussed below. Those limitations would have been aggravated severely by
-huge pages, because each tail page adds a refcount to the head page. And in
-fact, testing revealed that, without a separate compound_pincount field,
-page overflows were seen in some huge page stress tests.
-
-This also means that huge pages and compound pages do not suffer
+For large folios, the GUP_PIN_COUNTING_BIAS scheme is not used. Instead,
+the extra space available in the struct folio is used to store the
+pincount directly.
+
+This approach for large folios avoids the counting upper limit problems
+that are discussed below. Those limitations would have been aggravated
+severely by huge pages, because each tail page adds a refcount to the
+head page. And in fact, testing revealed that, without a separate pincount
+field, refcount overflows were seen in some huge page stress tests.
+
+This also means that huge pages and large folios do not suffer
from the false positives problem that is mentioned below.::
Function
@@ -264,9 +263,9 @@ place.)
Other diagnostics
=================
-dump_page() has been enhanced slightly, to handle these new counting
-fields, and to better report on compound pages in general. Specifically,
-for compound pages, the exact (compound_pincount) pincount is reported.
+dump_page() has been enhanced slightly to handle these new counting
+fields, and to better report on large folios in general. Specifically,
+for large folios, the exact pincount is reported.
References
==========
@@ -1011,11 +1011,6 @@ static inline void folio_set_compound_dtor(struct folio *folio,
void destroy_large_folio(struct folio *folio);
-static inline int head_compound_pincount(struct page *head)
-{
- return atomic_read(compound_pincount_ptr(head));
-}
-
static inline void set_compound_order(struct page *page, unsigned int order)
{
page[1].compound_order = order;
@@ -1641,11 +1636,6 @@ static inline struct folio *pfn_folio(unsigned long pfn)
return page_folio(pfn_to_page(pfn));
}
-static inline atomic_t *folio_pincount_ptr(struct folio *folio)
-{
- return &folio_page(folio, 1)->compound_pincount;
-}
-
/**
* folio_maybe_dma_pinned - Report if a folio may be pinned for DMA.
* @folio: The folio.
@@ -1663,7 +1653,7 @@ static inline atomic_t *folio_pincount_ptr(struct folio *folio)
* expected to be able to deal gracefully with a false positive.
*
* For large folios, the result will be exactly correct. That's because
- * we have more tracking data available: the compound_pincount is used
+ * we have more tracking data available: the _pincount field is used
* instead of the GUP_PIN_COUNTING_BIAS scheme.
*
* For more information, please see Documentation/core-api/pin_user_pages.rst.
@@ -1674,7 +1664,7 @@ static inline atomic_t *folio_pincount_ptr(struct folio *folio)
static inline bool folio_maybe_dma_pinned(struct folio *folio)
{
if (folio_test_large(folio))
- return atomic_read(folio_pincount_ptr(folio)) > 0;
+ return atomic_read(&folio->_pincount) > 0;
/*
* folio_ref_count() is signed. If that refcount overflows, then
@@ -443,11 +443,6 @@ static inline atomic_t *subpages_mapcount_ptr(struct page *page)
return &page[1].subpages_mapcount;
}
-static inline atomic_t *compound_pincount_ptr(struct page *page)
-{
- return &page[1].compound_pincount;
-}
-
/*
* Used for sizing the vmemmap region on some architectures
*/
@@ -94,11 +94,11 @@ static void __dump_page(struct page *page)
page, page_ref_count(head), mapcount, mapping,
page_to_pgoff(page), page_to_pfn(page));
if (compound) {
- pr_warn("head:%p order:%u compound_mapcount:%d subpages_mapcount:%d compound_pincount:%d\n",
+ pr_warn("head:%p order:%u compound_mapcount:%d subpages_mapcount:%d pincount:%d\n",
head, compound_order(head),
head_compound_mapcount(head),
head_subpages_mapcount(head),
- head_compound_pincount(head));
+ atomic_read(&folio->_pincount));
}
#ifdef CONFIG_MEMCG
@@ -111,7 +111,7 @@ static inline struct folio *try_get_folio(struct page *page, int refs)
* FOLL_GET: folio's refcount will be incremented by @refs.
*
* FOLL_PIN on large folios: folio's refcount will be incremented by
- * @refs, and its compound_pincount will be incremented by @refs.
+ * @refs, and its pincount will be incremented by @refs.
*
* FOLL_PIN on single-page folios: folio's refcount will be incremented by
* @refs * GUP_PIN_COUNTING_BIAS.
@@ -157,7 +157,7 @@ struct folio *try_grab_folio(struct page *page, int refs, unsigned int flags)
* try_get_folio() is left intact.
*/
if (folio_test_large(folio))
- atomic_add(refs, folio_pincount_ptr(folio));
+ atomic_add(refs, &folio->_pincount);
else
folio_ref_add(folio,
refs * (GUP_PIN_COUNTING_BIAS - 1));
@@ -182,7 +182,7 @@ static void gup_put_folio(struct folio *folio, int refs, unsigned int flags)
if (flags & FOLL_PIN) {
node_stat_mod_folio(folio, NR_FOLL_PIN_RELEASED, refs);
if (folio_test_large(folio))
- atomic_sub(refs, folio_pincount_ptr(folio));
+ atomic_sub(refs, &folio->_pincount);
else
refs *= GUP_PIN_COUNTING_BIAS;
}
@@ -232,7 +232,7 @@ int __must_check try_grab_page(struct page *page, unsigned int flags)
*/
if (folio_test_large(folio)) {
folio_ref_add(folio, 1);
- atomic_add(1, folio_pincount_ptr(folio));
+ atomic_add(1, &folio->_pincount);
} else {
folio_ref_add(folio, GUP_PIN_COUNTING_BIAS);
}
@@ -2477,9 +2477,9 @@ static void __split_huge_page_tail(struct page *head, int tail,
* of swap cache pages that store the swp_entry_t in tail pages.
* Fix up and warn once if private is unexpectedly set.
*
- * What of 32-bit systems, on which head[1].compound_pincount overlays
+ * What of 32-bit systems, on which folio->_pincount overlays
* head[1].private? No problem: THP_SWAP is not enabled on 32-bit, and
- * compound_pincount must be 0 for folio_ref_freeze() to have succeeded.
+ * pincount must be 0 for folio_ref_freeze() to have succeeded.
*/
if (!folio_test_swapcache(page_folio(head))) {
VM_WARN_ON_ONCE_PAGE(page_tail->private != 0, page_tail);
@@ -1476,7 +1476,7 @@ static void __destroy_compound_gigantic_folio(struct folio *folio,
atomic_set(folio_mapcount_ptr(folio), 0);
atomic_set(folio_subpages_mapcount_ptr(folio), 0);
- atomic_set(folio_pincount_ptr(folio), 0);
+ atomic_set(&folio->_pincount, 0);
for (i = 1; i < nr_pages; i++) {
p = folio_page(folio, i);
@@ -1998,7 +1998,7 @@ static bool __prep_compound_gigantic_folio(struct folio *folio,
}
atomic_set(folio_mapcount_ptr(folio), -1);
atomic_set(folio_subpages_mapcount_ptr(folio), 0);
- atomic_set(folio_pincount_ptr(folio), 0);
+ atomic_set(&folio->_pincount, 0);
return true;
out_error:
@@ -775,11 +775,13 @@ void free_compound_page(struct page *page)
static void prep_compound_head(struct page *page, unsigned int order)
{
+ struct folio *folio = (struct folio *)page;
+
set_compound_page_dtor(page, COMPOUND_PAGE_DTOR);
set_compound_order(page, order);
atomic_set(compound_mapcount_ptr(page), -1);
atomic_set(subpages_mapcount_ptr(page), 0);
- atomic_set(compound_pincount_ptr(page), 0);
+ atomic_set(&folio->_pincount, 0);
}
static void prep_compound_tail(struct page *head, int tail_idx)
@@ -1291,6 +1293,7 @@ static inline bool free_page_is_bad(struct page *page)
static int free_tail_pages_check(struct page *head_page, struct page *page)
{
+ struct folio *folio = (struct folio *)head_page;
int ret = 1;
/*
@@ -1314,8 +1317,8 @@ static int free_tail_pages_check(struct page *head_page, struct page *page)
bad_page(page, "nonzero subpages_mapcount");
goto out;
}
- if (unlikely(head_compound_pincount(head_page))) {
- bad_page(page, "nonzero compound_pincount");
+ if (unlikely(atomic_read(&folio->_pincount))) {
+ bad_page(page, "nonzero pincount");
goto out;
}
break;
We can use folio->_pincount directly, since all users are guarded by tests of compound/large. Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org> --- Documentation/core-api/pin_user_pages.rst | 29 +++++++++++------------ include/linux/mm.h | 14 ++--------- include/linux/mm_types.h | 5 ---- mm/debug.c | 4 ++-- mm/gup.c | 8 +++---- mm/huge_memory.c | 4 ++-- mm/hugetlb.c | 4 ++-- mm/page_alloc.c | 9 ++++--- 8 files changed, 32 insertions(+), 45 deletions(-)