Implement page discard using rcu. Each page has built-in entry rcu_head
that could be used to free the page from rcu.
Regarding the commant that "re-allocating the pages can result in
writeback deadlocks under heavy load" - if the user is in the risk of such
deadlocks, he should mount the filesystem without "-o discard".
Signed-off-by: Mikulas Patocka <mpato...@redhat.com>
---
drivers/block/brd.c | 30 ++++++++++++++++++------------
1 file changed, 18 insertions(+), 12 deletions(-)
Index: linux-2.6/drivers/block/brd.c
===================================================================
--- linux-2.6.orig/drivers/block/brd.c
+++ linux-2.6/drivers/block/brd.c
@@ -137,6 +137,12 @@ static struct page *brd_insert_page(stru
return page;
}
+static void brd_free_page_rcu(struct rcu_head *head)
+{
+ struct page *page = container_of(head, struct page, rcu_head);
+ __free_page(page);
+}
+
static void brd_free_page(struct brd_device *brd, sector_t sector)
{
struct page *page;
@@ -147,7 +153,7 @@ static void brd_free_page(struct brd_dev
page = radix_tree_delete(&brd->brd_pages, idx);
spin_unlock(&brd->brd_lock);
if (page)
- __free_page(page);
+ call_rcu(&page->rcu_head, brd_free_page_rcu);
}
static void brd_zero_page(struct brd_device *brd, sector_t sector)
@@ -233,7 +239,7 @@ static void discard_from_brd(struct brd_
* re-allocating the pages can result in writeback
* deadlocks under heavy load.
*/
- if (0)
+ if (1)
brd_free_page(brd, sector);
else
brd_zero_page(brd, sector);
@@ -257,22 +263,22 @@ static void copy_to_brd(struct brd_devic
copy = min_t(size_t, n, PAGE_SIZE - offset);
page = brd_lookup_page(brd, sector);
- BUG_ON(!page);
-
- dst = kmap_atomic(page);
- memcpy(dst + offset, src, copy);
- kunmap_atomic(dst);
+ if (page) {
+ dst = kmap_atomic(page);
+ memcpy(dst + offset, src, copy);
+ kunmap_atomic(dst);
+ }
if (copy < n) {
src += copy;
sector += copy >> SECTOR_SHIFT;
copy = n - copy;
page = brd_lookup_page(brd, sector);
- BUG_ON(!page);
-
- dst = kmap_atomic(page);
- memcpy(dst, src, copy);
- kunmap_atomic(dst);
+ if (page) {
+ dst = kmap_atomic(page);
+ memcpy(dst, src, copy);
+ kunmap_atomic(dst);
+ }
}
rcu_read_unlock();
--
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