Re: [RFC PATCH] mm: silence soft lockups from unlock_page

[Matthew Wilcox]

On Fri, Aug 07, 2020 at 11:41:09AM -0700, Hugh Dickins wrote:
> My home testing was, effectively, on top of c6fe44d96fc1 (v5.8 plus
> your two patches): I did not have in the io_uring changes from the
> current tree. In glancing there, I noticed one new and one previous
> instance of SetPageWaiters() *after* __add_wait_queue_entry_tail():
> are those correct?

By the way, don't do any performance testing on current Linus tree.
This commit:

commit 37f4a24c2469a10a4c16c641671bd766e276cf9f (refs/bisect/bad)
Author: Ming Lei <ming.lei@xxxxxxxxxx>
Date:   Tue Jun 30 22:03:57 2020 +0800

    blk-mq: centralise related handling into blk_mq_get_driver_tag
    
    Move .nr_active update and request assignment into blk_mq_get_driver_tag(),
    all are good to do during getting driver tag.
    
    Meantime blk-flush related code is simplified and flush request needn't
    to update the request table manually any more.
    
    Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx>
    Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>
    Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>

slows everything down, at least on my test qemu system.  Seems like it's
losing block queue tags.