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memfd: Convert memfd_wait_for_pins to XArray 

Simplify the locking by taking the spinlock while we walk the tree on
the assumption that many acquires and releases of the lock will be worse
than holding the lock while we process an entire batch of pages.

Signed-off-by: Matthew Wilcox <willy@infradead.org>
Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
This commit is contained in:
Matthew Wilcox 2017-11-22 11:11:31 -05:00
parent 7ae3424fb4
commit 2313216f86
1 changed files with 25 additions and 36 deletions
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61
mm/memfd.c
View File

@ -21,7 +21,7 @@
#include <uapi/linux/memfd.h>
/*
* We need a tag: a new tag would expand every radix_tree_node by 8 bytes,
* We need a tag: a new tag would expand every xa_node by 8 bytes,
* so reuse a tag which we firmly believe is never set or cleared on tmpfs
* or hugetlbfs because they are memory only filesystems.
*/
@ -72,9 +72,7 @@ static void memfd_tag_pins(struct address_space *mapping)
*/
static int memfd_wait_for_pins(struct address_space *mapping)
{
struct radix_tree_iter iter;
void __rcu **slot;
pgoff_t start;
XA_STATE(xas, &mapping->i_pages, 0);
struct page *page;
int error, scan;
@ -82,7 +80,9 @@ static int memfd_wait_for_pins(struct address_space *mapping)
error = 0;
for (scan = 0; scan <= LAST_SCAN; scan++) {
if (!radix_tree_tagged(&mapping->i_pages, MEMFD_TAG_PINNED))
unsigned int tagged = 0;
if (!xas_marked(&xas, MEMFD_TAG_PINNED))
break;
if (!scan)
@ -90,45 +90,34 @@ static int memfd_wait_for_pins(struct address_space *mapping)
else if (schedule_timeout_killable((HZ << scan) / 200))
scan = LAST_SCAN;
start = 0;
rcu_read_lock();
radix_tree_for_each_tagged(slot, &mapping->i_pages, &iter,
start, MEMFD_TAG_PINNED) {
page = radix_tree_deref_slot(slot);
if (radix_tree_exception(page)) {
if (radix_tree_deref_retry(page)) {
slot = radix_tree_iter_retry(&iter);
continue;
}
page = NULL;
}
if (page &&
page_count(page) - page_mapcount(page) != 1) {
if (scan < LAST_SCAN)
goto continue_resched;
xas_set(&xas, 0);
xas_lock_irq(&xas);
xas_for_each_marked(&xas, page, ULONG_MAX, MEMFD_TAG_PINNED) {
bool clear = true;
if (xa_is_value(page))
continue;
if (page_count(page) - page_mapcount(page) != 1) {
/*
* On the last scan, we clean up all those tags
* we inserted; but make a note that we still
* found pages pinned.
*/
error = -EBUSY;
if (scan == LAST_SCAN)
error = -EBUSY;
else
clear = false;
}
if (clear)
xas_clear_mark(&xas, MEMFD_TAG_PINNED);
if (++tagged % XA_CHECK_SCHED)
continue;
xa_lock_irq(&mapping->i_pages);
radix_tree_tag_clear(&mapping->i_pages,
iter.index, MEMFD_TAG_PINNED);
xa_unlock_irq(&mapping->i_pages);
continue_resched:
if (need_resched()) {
slot = radix_tree_iter_resume(slot, &iter);
cond_resched_rcu();
}
xas_pause(&xas);
xas_unlock_irq(&xas);
cond_resched();
xas_lock_irq(&xas);
}
rcu_read_unlock();
xas_unlock_irq(&xas);
}
return error;