From: Minchan Kim <minchan@xxxxxxxxxx> Subject: mm/page_io.c: annotate refault stalls from swap_readpage If a block device supports rw_page operation, it doesn't submit bios so the 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. [akpm@xxxxxxxxxxxxxxxxxxxx: add comment, per Johannes] Link: http://lkml.kernel.org/r/20191010152134.38545-1-minchan@xxxxxxxxxx Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx> Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx> Reviewed-by: Shakeel Butt <shakeelb@xxxxxxxxxx> Cc: Seth Jennings <sjenning@xxxxxxxxxx> Cc: Dan Streetman <ddstreet@xxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/page_io.c | 15 +++++++++++++-- 1 file changed, 13 insertions(+), 2 deletions(-) --- a/mm/page_io.c~mm-annotate-refault-stalls-from-swap_readpage +++ a/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 +355,19 @@ int swap_readpage(struct page *page, boo 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, + * or the submitting cgroup IO-throttled, 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 +381,7 @@ int swap_readpage(struct page *page, boo 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 +392,7 @@ int swap_readpage(struct page *page, boo } count_vm_event(PSWPIN); - return 0; + goto out; } ret = 0; @@ -418,6 +428,7 @@ int swap_readpage(struct page *page, boo bio_put(bio); out: + psi_memstall_leave(&pflags); return ret; } _
