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Date: Tue, 7 Jul 2020 23:18:12 +0100
From: Matthew Wilcox <willy@...radead.org>
To: Jens Axboe <axboe@...nel.dk>
Cc: Kanchan Joshi <joshi.k@...sung.com>, viro@...iv.linux.org.uk,
bcrl@...ck.org, hch@...radead.org, Damien.LeMoal@....com,
asml.silence@...il.com, linux-fsdevel@...r.kernel.org,
mb@...htnvm.io, linux-kernel@...r.kernel.org, linux-aio@...ck.org,
io-uring@...r.kernel.org, linux-block@...r.kernel.org,
Selvakumar S <selvakuma.s1@...sung.com>,
Nitesh Shetty <nj.shetty@...sung.com>,
Javier Gonzalez <javier.gonz@...sung.com>
Subject: Re: [PATCH v3 4/4] io_uring: add support for zone-append
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:
+#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;
+}
... etc, also need an unregister.
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