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Tue, 07 Jul 2020 15:37:58 -0700 (PDT) Subject: Re: [PATCH v3 4/4] io_uring: add support for zone-append To: Matthew Wilcox Cc: Kanchan Joshi , viro@zeniv.linux.org.uk, bcrl@kvack.org, hch@infradead.org, Damien.LeMoal@wdc.com, asml.silence@gmail.com, linux-fsdevel@vger.kernel.org, mb@lightnvm.io, linux-kernel@vger.kernel.org, linux-aio@kvack.org, io-uring@vger.kernel.org, linux-block@vger.kernel.org, Selvakumar S , Nitesh Shetty , Javier Gonzalez References: <20200705210947.GW25523@casper.infradead.org> <239ee322-9c38-c838-a5b2-216787ad2197@kernel.dk> <20200706141002.GZ25523@casper.infradead.org> <4a9bf73e-f3ee-4f06-7fad-b8f8861b0bc1@kernel.dk> <20200706143208.GA25523@casper.infradead.org> <20200707151105.GA23395@test-zns> <20200707155237.GM25523@casper.infradead.org> <20200707202342.GA28364@test-zns> <7a44d9c6-bf7d-0666-fc29-32c3cba9d1d8@kernel.dk> <20200707221812.GN25523@casper.infradead.org> From: Jens Axboe Message-ID: <145cc0ad-af86-2d6a-78b3-9ade007aae52@kernel.dk> Date: Tue, 7 Jul 2020 16:37:55 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.8.0 MIME-Version: 1.0 In-Reply-To: <20200707221812.GN25523@casper.infradead.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On 7/7/20 4:18 PM, Matthew Wilcox wrote: > On Tue, Jul 07, 2020 at 02:40:06PM -0600, Jens Axboe wrote: >>>> so we have another 24 bytes before io_kiocb takes up another cacheline. >>>> If that's a serious problem, I have an idea about how to shrink struct >>>> kiocb by 8 bytes so struct io_rw would have space to store another >>>> pointer. >>> Yes, io_kiocb has room. Cache-locality wise whether that is fine or >>> it must be placed within io_rw - I'll come to know once I get to >>> implement this. Please share the idea you have, it can come handy. >> >> Except it doesn't, I'm not interested in adding per-request type fields >> to the generic part of it. Before we know it, we'll blow past the next >> cacheline. >> >> If we can find space in the kiocb, that'd be much better. Note that once >> the async buffered bits go in for 5.9, then there's no longer a 4-byte >> hole in struct kiocb. > > Well, poot, I was planning on using that. OK, how about this: Figured you might have had your sights set on that one, which is why I wanted to bring it up upfront :-) > +#define IOCB_NO_CMPL (15 << 28) > > struct kiocb { > [...] > - void (*ki_complete)(struct kiocb *iocb, long ret, long ret2); > + loff_t __user *ki_uposp; > - int ki_flags; > + unsigned int ki_flags; > > +typedef void ki_cmpl(struct kiocb *, long ret, long ret2); > +static ki_cmpl * const ki_cmpls[15]; > > +void ki_complete(struct kiocb *iocb, long ret, long ret2) > +{ > + unsigned int id = iocb->ki_flags >> 28; > + > + if (id < 15) > + ki_cmpls[id](iocb, ret, ret2); > +} > > +int kiocb_cmpl_register(void (*cb)(struct kiocb *, long, long)) > +{ > + for (i = 0; i < 15; i++) { > + if (ki_cmpls[id]) > + continue; > + ki_cmpls[id] = cb; > + return id; > + } > + WARN(); > + return -1; > +} That could work, we don't really have a lot of different completion types in the kernel. -- Jens Axboe