The patch titled
Subject: mm/memfd: refactor memfd_tag_pins() and memfd_wait_for_pins()
has been added to the -mm mm-unstable branch. Its filename is
mm-memfd-refactor-memfd_tag_pins-and-memfd_wait_for_pins.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-memfd-refactor-memfd_tag_pins-and-memfd_wait_for_pins.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: David Hildenbrand <david@xxxxxxxxxx>
Subject: mm/memfd: refactor memfd_tag_pins() and memfd_wait_for_pins()
Date: Mon, 26 Feb 2024 15:13:23 +0100
Patch series "mm: remove total_mapcount()", v2.
Let's remove the remaining user from mm/memfd.c so we can get rid of
total_mapcount().
This patch (of 2):
Both functions are the remaining users of total_mapcount(). Let's get rid
of the calls by converting the code to folios.
As it turns out, the code is unnecessarily complicated, especially:
1) We can query the number of pagecache references for a folio simply via
folio_nr_pages(). This will handle other folio sizes in the future
correctly.
2) The xas_set(xas, page->index + cache_count) call to increment the
iterator for large folios is not required. Remove it.
Further, simplify the XA_CHECK_SCHED check, counting each entry exactly
once.
Memfd pages can be swapped out when using shmem; leave xa_is_value()
checks in place.
Link: https://lkml.kernel.org/r/20240226141324.278526-1-david@xxxxxxxxxx
Link: https://lkml.kernel.org/r/20240226141324.278526-2-david@xxxxxxxxxx
Co-developed-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
Reviewed-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/memfd.c | 47 ++++++++++++++++++-----------------------------
1 file changed, 18 insertions(+), 29 deletions(-)
--- a/mm/memfd.c~mm-memfd-refactor-memfd_tag_pins-and-memfd_wait_for_pins
+++ a/mm/memfd.c
@@ -29,29 +29,25 @@
#define MEMFD_TAG_PINNED PAGECACHE_TAG_TOWRITE
#define LAST_SCAN 4 /* about 150ms max */
+static bool memfd_folio_has_extra_refs(struct folio *folio)
+{
+ return folio_ref_count(folio) - folio_mapcount(folio) !=
+ folio_nr_pages(folio);
+}
+
static void memfd_tag_pins(struct xa_state *xas)
{
- struct page *page;
+ struct folio *folio;
int latency = 0;
- int cache_count;
lru_add_drain();
xas_lock_irq(xas);
- xas_for_each(xas, page, ULONG_MAX) {
- cache_count = 1;
- if (!xa_is_value(page) &&
- PageTransHuge(page) && !PageHuge(page))
- cache_count = HPAGE_PMD_NR;
-
- if (!xa_is_value(page) &&
- page_count(page) - total_mapcount(page) != cache_count)
+ xas_for_each(xas, folio, ULONG_MAX) {
+ if (!xa_is_value(folio) && memfd_folio_has_extra_refs(folio))
xas_set_mark(xas, MEMFD_TAG_PINNED);
- if (cache_count != 1)
- xas_set(xas, page->index + cache_count);
- latency += cache_count;
- if (latency < XA_CHECK_SCHED)
+ if (++latency < XA_CHECK_SCHED)
continue;
latency = 0;
@@ -66,16 +62,16 @@ static void memfd_tag_pins(struct xa_sta
/*
* Setting SEAL_WRITE requires us to verify there's no pending writer. However,
* via get_user_pages(), drivers might have some pending I/O without any active
- * user-space mappings (eg., direct-IO, AIO). Therefore, we look at all pages
+ * user-space mappings (eg., direct-IO, AIO). Therefore, we look at all folios
* and see whether it has an elevated ref-count. If so, we tag them and wait for
* them to be dropped.
* The caller must guarantee that no new user will acquire writable references
- * to those pages to avoid races.
+ * to those folios to avoid races.
*/
static int memfd_wait_for_pins(struct address_space *mapping)
{
XA_STATE(xas, &mapping->i_pages, 0);
- struct page *page;
+ struct folio *folio;
int error, scan;
memfd_tag_pins(&xas);
@@ -83,7 +79,6 @@ static int memfd_wait_for_pins(struct ad
error = 0;
for (scan = 0; scan <= LAST_SCAN; scan++) {
int latency = 0;
- int cache_count;
if (!xas_marked(&xas, MEMFD_TAG_PINNED))
break;
@@ -95,20 +90,15 @@ static int memfd_wait_for_pins(struct ad
xas_set(&xas, 0);
xas_lock_irq(&xas);
- xas_for_each_marked(&xas, page, ULONG_MAX, MEMFD_TAG_PINNED) {
+ xas_for_each_marked(&xas, folio, ULONG_MAX, MEMFD_TAG_PINNED) {
bool clear = true;
- cache_count = 1;
- if (!xa_is_value(page) &&
- PageTransHuge(page) && !PageHuge(page))
- cache_count = HPAGE_PMD_NR;
-
- if (!xa_is_value(page) && cache_count !=
- page_count(page) - total_mapcount(page)) {
+ if (!xa_is_value(folio) &&
+ memfd_folio_has_extra_refs(folio)) {
/*
* On the last scan, we clean up all those tags
* we inserted; but make a note that we still
- * found pages pinned.
+ * found folios pinned.
*/
if (scan == LAST_SCAN)
error = -EBUSY;
@@ -118,8 +108,7 @@ static int memfd_wait_for_pins(struct ad
if (clear)
xas_clear_mark(&xas, MEMFD_TAG_PINNED);
- latency += cache_count;
- if (latency < XA_CHECK_SCHED)
+ if (++latency < XA_CHECK_SCHED)
continue;
latency = 0;
_
Patches currently in -mm which might be from david@xxxxxxxxxx are
mm-memfd-refactor-memfd_tag_pins-and-memfd_wait_for_pins.patch
mm-remove-total_mapcount.patch
