On Thu, Oct 10, 2019 at 03:17:47PM -0400, Johannes Weiner wrote:
> On Thu, Oct 10, 2019 at 08:21:34AM -0700, Minchan Kim wrote:
> > From: Minchan Kim <minchan@xxxxxxxxxx>
> >
> > 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 <hannes@xxxxxxxxxxx>
> > Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
>
> Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>
Thanks, Johannes!
>
> Can you please add a comment to the caller? Lifted from submit_bio():
Sure, I added a little about zram.
>
> /*
> * Count submission time as memory stall. When the device is
> * congested, or the submitting cgroup IO-throttled,
> * submission can be a significant part of overall IO time.
> */
>From a8ae7cbc2d3f050aca810fd68285d45cb933b825 Mon Sep 17 00:00:00 2001
From: Minchan Kim <minchan@xxxxxxxxxx>
Date: Thu, 10 Oct 2019 08:09:06 -0700
Subject: [PATCH v2] mm: annotate refault stalls from swap_readpage
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.
Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>
Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
---
mm/page_io.c | 16 ++++++++++++++--
1 file changed, 14 insertions(+), 2 deletions(-)
diff --git a/mm/page_io.c b/mm/page_io.c
index 24ee600f9131..18f1f8e1d27f 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 +355,20 @@ 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);
+
+ /*
+ * Count submission time as memory stall. When the device is
+ * congested, the submitting cgroup IO-throttled, or backing
+ * device works synchronously(e.g., zram), submission can be
+ * a significant part of overall IO time.
+ */
+ psi_memstall_enter(&pflags);
+
if (frontswap_load(page) == 0) {
SetPageUptodate(page);
unlock_page(page);
@@ -371,7 +382,7 @@ 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 +393,7 @@ int swap_readpage(struct page *page, bool synchronous)
}
count_vm_event(PSWPIN);
- return 0;
+ goto out;
}
ret = 0;
@@ -418,6 +429,7 @@ int swap_readpage(struct page *page, bool synchronous)
bio_put(bio);
out:
+ psi_memstall_leave(&pflags);
return ret;
}
--
2.23.0.581.g78d2f28ef7-goog
