superrob1500
/
mirror-linux
mirror of https://github.com/torvalds/linux
1
0
Fork 0
Code Issues Packages Projects Releases Wiki Activity

brd: use page reference to protect page lifetime 

As discussed [1], hold rcu for copying data from/to page is too heavy,
it's better to protect page with rcu around for page lookup and then
grab a reference to prevent page to be freed by discard.

[1] https://lore.kernel.org/all/eb41cab3-5946-4fe3-a1be-843dd6fca159@kernel.dk/

Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Link: https://lore.kernel.org/r/20250811065628.1829339-1-yukuai1@huaweicloud.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
pull/1354/merge
Yu Kuai 2025-08-11 14:56:28 +08:00 committed by Jens Axboe
parent 4c7ef92f6d
commit 2a06145228
1 changed files with 48 additions and 27 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

75
drivers/block/brd.c
View File

@ -44,45 +44,74 @@ struct brd_device {
};
/*
* Look up and return a brd's page for a given sector.
* Look up and return a brd's page with reference grabbed for a given sector.
*/
static struct page *brd_lookup_page(struct brd_device *brd, sector_t sector)
{
return xa_load(&brd->brd_pages, sector >> PAGE_SECTORS_SHIFT);
struct page *page;
XA_STATE(xas, &brd->brd_pages, sector >> PAGE_SECTORS_SHIFT);
rcu_read_lock();
repeat:
page = xas_load(&xas);
if (xas_retry(&xas, page)) {
xas_reset(&xas);
goto repeat;
}
if (!page)
goto out;
if (!get_page_unless_zero(page)) {
xas_reset(&xas);
goto repeat;
}
if (unlikely(page != xas_reload(&xas))) {
put_page(page);
xas_reset(&xas);
goto repeat;
}
out:
rcu_read_unlock();
return page;
}
/*
* Insert a new page for a given sector, if one does not already exist.
* The returned page will grab reference.
*/
static struct page *brd_insert_page(struct brd_device *brd, sector_t sector,
blk_opf_t opf)
__releases(rcu)
__acquires(rcu)
{
gfp_t gfp = (opf & REQ_NOWAIT) ? GFP_NOWAIT : GFP_NOIO;
struct page *page, *ret;
rcu_read_unlock();
page = alloc_page(gfp | __GFP_ZERO | __GFP_HIGHMEM);
if (!page) {
rcu_read_lock();
if (!page)
return ERR_PTR(-ENOMEM);
}
xa_lock(&brd->brd_pages);
ret = __xa_cmpxchg(&brd->brd_pages, sector >> PAGE_SECTORS_SHIFT, NULL,
page, gfp);
rcu_read_lock();
if (ret) {
if (!ret) {
brd->brd_nr_pages++;
get_page(page);
xa_unlock(&brd->brd_pages);
__free_page(page);
if (xa_is_err(ret))
return ERR_PTR(xa_err(ret));
return page;
}
if (!xa_is_err(ret)) {
get_page(ret);
xa_unlock(&brd->brd_pages);
put_page(page);
return ret;
}
brd->brd_nr_pages++;
xa_unlock(&brd->brd_pages);
return page;
put_page(page);
return ERR_PTR(xa_err(ret));
}
/*
@ -95,7 +124,7 @@ static void brd_free_pages(struct brd_device *brd)
pgoff_t idx;
xa_for_each(&brd->brd_pages, idx, page) {
__free_page(page);
put_page(page);
cond_resched();
}
@ -117,7 +146,6 @@ static bool brd_rw_bvec(struct brd_device *brd, struct bio *bio)
bv.bv_len = min_t(u32, bv.bv_len, PAGE_SIZE - offset);
rcu_read_lock();
page = brd_lookup_page(brd, sector);
if (!page && op_is_write(opf)) {
page = brd_insert_page(brd, sector, opf);
@ -135,13 +163,13 @@ static bool brd_rw_bvec(struct brd_device *brd, struct bio *bio)
memset(kaddr, 0, bv.bv_len);
}
kunmap_local(kaddr);
rcu_read_unlock();
bio_advance_iter_single(bio, &bio->bi_iter, bv.bv_len);
if (page)
put_page(page);
return true;
out_error:
rcu_read_unlock();
if (PTR_ERR(page) == -ENOMEM && (opf & REQ_NOWAIT))
bio_wouldblock_error(bio);
else
@ -149,13 +177,6 @@ out_error:
return false;
}
static void brd_free_one_page(struct rcu_head *head)
{
struct page *page = container_of(head, struct page, rcu_head);
__free_page(page);
}
static void brd_do_discard(struct brd_device *brd, sector_t sector, u32 size)
{
sector_t aligned_sector = round_up(sector, PAGE_SECTORS);
@ -170,7 +191,7 @@ static void brd_do_discard(struct brd_device *brd, sector_t sector, u32 size)
while (aligned_sector < aligned_end && aligned_sector < rd_size * 2) {
page = __xa_erase(&brd->brd_pages, aligned_sector >> PAGE_SECTORS_SHIFT);
if (page) {
call_rcu(&page->rcu_head, brd_free_one_page);
put_page(page);
brd->brd_nr_pages--;
}
aligned_sector += PAGE_SECTORS;