Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Fri, 7 Aug 2020 20:35:10 +0100
From:   Matthew Wilcox <willy@infradead.org>
To:     Hugh Dickins <hughd@google.com>
Cc:     Linus Torvalds <torvalds@linux-foundation.org>,
        Oleg Nesterov <oleg@redhat.com>,
        Michal Hocko <mhocko@kernel.org>,
        Linux-MM <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Tim Chen <tim.c.chen@linux.intel.com>,
        Michal Hocko <mhocko@suse.com>,
        Greg KH <gregkh@linuxfoundation.org>
Subject: Re: [RFC PATCH] mm: silence soft lockups from unlock_page
Message-ID: <20200807193510.GG17456@casper.infradead.org>
References: <20200725101445.GB3870@redhat.com>
 <CAHk-=whSJbODMVmxxDs64f7BaESKWuMqOxWGpjUSDn6Jzqa71g@mail.gmail.com>
 <alpine.LSU.2.11.2007251343370.3804@eggly.anvils>
 <alpine.LSU.2.11.2007252100230.5376@eggly.anvils>
 <alpine.LSU.2.11.2007261246530.6812@eggly.anvils>
 <alpine.LSU.2.11.2008052105040.8716@eggly.anvils>
 <CAHk-=whf7wCUV2oTDUg0eeNafhhk_OhJBT2SbHZXwgtmAzNeTg@mail.gmail.com>
 <20200806180024.GB17456@casper.infradead.org>
 <CAHk-=wihTRHMm1LC4AfidZptT9ZuT-wBjE2VhYzKBy66e4iwQw@mail.gmail.com>
 <alpine.LSU.2.11.2008071047510.1239@eggly.anvils>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <alpine.LSU.2.11.2008071047510.1239@eggly.anvils>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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@redhat.com>
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@redhat.com>
    Cc: Christoph Hellwig <hch@infradead.org>
    Signed-off-by: Jens Axboe <axboe@kernel.dk>

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