Once upon a time, all swapins counted toward memory pressure[1]. Then
Joonsoo introduced workingset detection for anonymous pages and we
gained the ability to distinguish hot from cold swapins[2][3]. But we
failed to update swap_readpage() accordingly, and now we account
partial memory pressure in the swapin path of cold memory.
Not for all situations - which adds more inconsistency: paths using
the conventional submit_bio() and lock_page() route will not see much
pressure - unless storage itself is heavily congested and the bio
submissions stall. ZRAM and ZSWAP do most of the work directly from
swap_readpage() and will see all swapins reflected as pressure.
Restore consistency by making all swapin stall accounting conditional
on the page actually being part of the workingset.
[1] commit 937790699be9 ("mm/page_io.c: annotate refault stalls from swap_readpage")
[2] commit aae466b0052e ("mm/swap: implement workingset detection for anonymous LRU")
[3] commit cad8320b4b39 ("mm/swap: don't SetPageWorkingset unconditionally during swapin")
Reported-by: CGEL <cgel.zte@xxxxxxxxx>
Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Minchan Kim <minchan@xxxxxxxxxx>
Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Cc: Yu Zhao <yuzhao@xxxxxxxxxx>
---
mm/page_io.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)
diff --git a/mm/page_io.c b/mm/page_io.c
index 61c792f916fa..f6296ee25014 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -359,6 +359,7 @@ int swap_readpage(struct page *page, bool synchronous)
struct bio *bio;
int ret = 0;
struct swap_info_struct *sis = page_swap_info(page);
+ bool workingset = PageWorkingset(page);
unsigned long pflags;
VM_BUG_ON_PAGE(!PageSwapCache(page) && !synchronous, page);
@@ -370,7 +371,8 @@ int swap_readpage(struct page *page, bool synchronous)
* or the submitting cgroup IO-throttled, submission can be a
* significant part of overall IO time.
*/
- psi_memstall_enter(&pflags);
+ if (workingset)
+ psi_memstall_enter(&pflags);
delayacct_swapin_start();
if (frontswap_load(page) == 0) {
@@ -431,7 +433,8 @@ int swap_readpage(struct page *page, bool synchronous)
bio_put(bio);
out:
- psi_memstall_leave(&pflags);
+ if (workingset)
+ psi_memstall_leave(&pflags);
delayacct_swapin_end();
return ret;
}
--
2.34.1
