linux-kernel - Re: Expense of read

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Message-ID: <alpine.LRH.2.02.2101211101190.18413@file01.intranet.prod.int.rdu2.redhat.com>
Date:   Thu, 21 Jan 2021 11:06:10 -0500 (EST)
From:   Mikulas Patocka <mpatocka@...hat.com>
To:     Matthew Wilcox <willy@...radead.org>
cc:     Jan Kara <jack@...e.cz>, Dave Chinner <david@...morbit.com>,
        Zhongwei Cai <sunrise_l@...u.edu.cn>,
        "Theodore Ts'o" <tytso@....edu>,
        David Laight <David.Laight@...lab.com>,
        Mingkai Dong <mingkaidong@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Steven Whitehouse <swhiteho@...hat.com>,
        Eric Sandeen <esandeen@...hat.com>,
        Dave Chinner <dchinner@...hat.com>,
        Wang Jianchao <jianchao.wan9@...il.com>,
        Rajesh Tadakamadla <rajesh.tadakamadla@....com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        linux-nvdimm <linux-nvdimm@...ts.01.org>
Subject: Re: Expense of read_iter



On Thu, 21 Jan 2021, Matthew Wilcox wrote:

> On Wed, Jan 20, 2021 at 10:12:01AM -0500, Mikulas Patocka wrote:
> > Do you have some idea how to optimize the generic code that calls 
> > ->read_iter?
> 
> Yes.
> 
> > It might be better to maintain an f_iocb_flags in the
> > struct file and just copy that unconditionally.  We'd need to remember
> > to update it in fcntl(F_SETFL), but I think that's the only place.
> 
> Want to give that a try?

Yes - send me the patch and I'll benchmark it.

Mikulas