linux-kernel - Re: [PATCH] block: switch to atomic

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Message-ID: <17e7fcdc-4450-771a-a84b-b2a15b37c122@kernel.dk>
Date:   Mon, 6 Dec 2021 09:31:24 -0700
From:   Jens Axboe <axboe@...nel.dk>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>, keescook@...omium.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] block: switch to atomic_t for request references

On 12/5/21 11:53 PM, Christoph Hellwig wrote:
> On Fri, Dec 03, 2021 at 08:35:40AM -0700, Jens Axboe wrote:
>> refcount_t is not as expensive as it used to be, but it's still more
>> expensive than the io_uring method of using atomic_t and just checking
>> for potential over/underflow.
>>
>> This borrows that same implementation, which in turn is based on the
>> mm implementation from Linus.
> 
> If refcount_t isn't good enough for a normal kernel fast path we have
> a problem.  Can we discuss that with the maintainers instead of coming
> up with our home grown schemes again?

I think what needs to happen next here is that the code is put into a
separate header so that the vm, io_uring, and block can all use it.
refcount_t is better than it used to be, but there's a difference
between fast path and tens of millions of inc/decs per second.

-- 
Jens Axboe