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Subject: Re: [RFC PATCH] locking/percpu-rwsem: use this_cpu_{inc|dec}() for
 read_count
To:     Matthew Wilcox <willy@infradead.org>,
        Oleg Nesterov <oleg@redhat.com>
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        Christoph Lameter <cl@linux.com>, linux-kernel@vger.kernel.org,
        linux-fsdevel@vger.kernel.org, Jan Kara <jack@suse.cz>
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From:   Boaz Harrosh <boaz@plexistor.com>
Message-ID: <e25a3354-04e4-54e9-a45f-7305bfd1f2bb@plexistor.com>
Date:   Thu, 17 Sep 2020 16:46:38 +0300
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On 17/09/2020 15:48, Matthew Wilcox wrote:
> On Thu, Sep 17, 2020 at 02:01:33PM +0200, Oleg Nesterov wrote:
<>
> 
> If we change bio_endio to invoke the ->bi_end_io callbacks in softirq
> context instead of hardirq context, we can change the pagecache to take
> BH-safe locks instead of IRQ-safe locks.  I believe the only reason the
> lock needs to be IRQ-safe is for the benefit of paths like:
> 

 From my totally subjective experience on the filesystem side (user of 
bio_endio) all HW block drivers I used including Nvme isci, sata... etc. 
end up calling bio_endio in softirq. The big exception to that is the 
vdX drivers under KVM. Which is very Ironic to me.
I wish we could make all drivers be uniform in this regard.

But maybe I'm just speaking crap. Its only from my limited debuging 
expirience.

Thanks
Boaz