[PATCH] mm: annotate refault stalls from swap_readpage

[Minchan Kim]

From: Minchan Kim <minc...@google.com>

If block device supports rw_page operation, it doesn't submit bio
so annotation in submit_bio for refault stall doesn't work.
It happens with zram in android, especially swap read path which
could consume CPU cycle for decompress. It is also a problem for
zswap which uses frontswap.

Annotate swap_readpage() to account the synchronous IO overhead
to prevent underreport memory pressure.

Cc: Johannes Weiner <han...@cmpxchg.org>
Signed-off-by: Minchan Kim <minc...@google.com>
---
 mm/page_io.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/mm/page_io.c b/mm/page_io.c
index 24ee600f9131..20147473d4a5 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -22,6 +22,7 @@
 #include <linux/writeback.h>
 #include <linux/frontswap.h>
 #include <linux/blkdev.h>
+#include <linux/psi.h>
 #include <linux/uio.h>
 #include <linux/sched/task.h>
 #include <asm/pgtable.h>
@@ -354,10 +355,14 @@ int swap_readpage(struct page *page, bool synchronous)
        struct swap_info_struct *sis = page_swap_info(page);
        blk_qc_t qc;
        struct gendisk *disk;
+       unsigned long pflags;
 
        VM_BUG_ON_PAGE(!PageSwapCache(page) && !synchronous, page);
        VM_BUG_ON_PAGE(!PageLocked(page), page);
        VM_BUG_ON_PAGE(PageUptodate(page), page);
+
+       psi_memstall_enter(&pflags);
+
        if (frontswap_load(page) == 0) {
                SetPageUptodate(page);
                unlock_page(page);
@@ -371,7 +376,7 @@ int swap_readpage(struct page *page, bool synchronous)
                ret = mapping->a_ops->readpage(swap_file, page);
                if (!ret)
                        count_vm_event(PSWPIN);
-               return ret;
+               goto out;
        }
 
        ret = bdev_read_page(sis->bdev, swap_page_sector(page), page);
@@ -382,7 +387,7 @@ int swap_readpage(struct page *page, bool synchronous)
                }
 
                count_vm_event(PSWPIN);
-               return 0;
+               goto out;
        }
 
        ret = 0;
@@ -418,6 +423,7 @@ int swap_readpage(struct page *page, bool synchronous)
        bio_put(bio);
 
 out:
+       psi_memstall_leave(&pflags);
        return ret;
 }
 
-- 
2.23.0.581.g78d2f28ef7-goog