From: Jens Axboe <axboe@kernel.dk>
To: Al Viro <viro@zeniv.linux.org.uk>
Cc: Christoph Hellwig <hch@lst.de>,
Matthew Wilcox <willy@infradead.org>,
linux-fsdevel@vger.kernel.org
Subject: Re: [RFC] what to do with IOCB_DSYNC?
Date: Mon, 23 May 2022 09:12:32 -0600 [thread overview]
Message-ID: <6594c360-0c7c-412f-29c9-377ddda16937@kernel.dk> (raw)
In-Reply-To: <YoueZl4Zx0WUH3CS@zeniv-ca.linux.org.uk>
On 5/23/22 8:47 AM, Al Viro wrote:
> On Mon, May 23, 2022 at 08:34:44AM -0600, Jens Axboe wrote:
>> On 5/23/22 08:22, Al Viro wrote:
>>> On Sun, May 22, 2022 at 08:43:26PM -0600, Jens Axboe wrote:
>>>
>>>> Branch here:
>>>>
>>>> https://git.kernel.dk/cgit/linux-block/log/?h=iov-iter
>>>>
>>>> First 5 are generic ones, and some of them should just be folded with
>>>> your changes.
>>>>
>>>> Last 2 are just converting io_uring to use it where appropriate.
>>>>
>>>> We can also use it for vectored readv/writev and recvmsg/sendmsg with
>>>> one segment. The latter is mostly single segment in the real world
>>>> anyway, former probably too. Though not sure it's worth it when we're
>>>> copying a single iovec first anyway? Something to test...
>>>
>>> Not a good idea. Don't assume that all users of iov_iter are well-behaving;
>>> not everything is flavour-agnostic. If nothing else, you'll break the hell
>>> out of infinibarf - both qib and hfi check that ->write_iter() gets
>>> IOV_ITER target and fail otherwise.
>>
>> OK, I'll check up on that.
>>
>>> BTW, #work.iov_iter is going to be rebased and reordered; if nothing else,
>>> a bunch of places like
>>> dio->should_dirty = iter_is_iovec(iter) && iov_iter_rw(iter) == READ;
>>> need to be dealt with before we switch new_sync_read() and new_sync_write()
>>> to ITER_UBUF.
>>
>> I already made an attempt at that, see the git branch I sent in the last email.
>
> There's several more, AFAICS (cifs, ceph, fuse, gfs2)... The check in
> /dev/fuse turned out to be fine - it's only using primitives, so we
> can pass ITER_UBUF ones there. mm/shmem.c check... similar, but I
> really wonder if x86 clear_user() really sucks worse than
> copy_to_user() from zero page...
Yep, not surprised if it isn't complete, I just tackled the ones I
found. I do like the idea of having a generic check for that rather
than implicit knowledge about which iter types may contain user memory.
I haven't looked at clear_user() vs copy_to_user() from the zero page.
But should be trivial to benchmark and profile. I'll try and do that
when I find some time.
> FWIW, I'd added bool ->user_backed next to ->data_source, with
> user_backed_iter() as an inline predicate checking it. Seems to get
> slightly better iov_iter.c code generation that way...
OK that sounds fine too, I pondered doing something similar rather than
have the helper since there is an existing hole in there anyway.
> Current branch pushed to #new.iov_iter (at the moment; will rename
> back to work.iov_iter once it gets more or less stable).
Sounds good, I'll see what I need to rebase.
--
Jens Axboe
next prev parent reply other threads:[~2022-05-23 15:12 UTC|newest]
Thread overview: 60+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-21 0:46 [RFC] what to do with IOCB_DSYNC? Al Viro
2021-06-21 13:59 ` Christoph Hellwig
2021-06-21 14:03 ` Matthew Wilcox
2021-06-21 14:09 ` Christoph Hellwig
2021-06-21 14:16 ` Matthew Wilcox
2021-06-21 14:22 ` Christoph Hellwig
2021-06-21 14:32 ` Al Viro
2021-06-21 14:35 ` Christoph Hellwig
2021-06-21 15:22 ` Jens Axboe
2022-05-21 17:48 ` Al Viro
2022-05-21 19:03 ` Jens Axboe
2022-05-21 22:14 ` Jens Axboe
2022-05-22 7:45 ` Christoph Hellwig
2022-05-22 10:23 ` Matthew Wilcox
2022-05-22 10:36 ` Al Viro
2022-05-22 11:15 ` Matthew Wilcox
2022-05-22 11:45 ` Christoph Hellwig
2022-05-22 12:39 ` Jens Axboe
2022-05-22 12:48 ` Al Viro
2022-05-22 13:02 ` Jens Axboe
2022-05-22 13:07 ` Al Viro
2022-05-22 13:09 ` Jens Axboe
2022-05-22 18:06 ` Jens Axboe
2022-05-22 18:25 ` Al Viro
2022-05-22 18:29 ` Jens Axboe
2022-05-22 18:39 ` Al Viro
2022-05-22 18:48 ` Jens Axboe
2022-05-22 19:04 ` Al Viro
2022-05-22 20:03 ` Jens Axboe
2022-05-23 0:42 ` Al Viro
2022-05-23 1:22 ` Jens Axboe
2022-05-23 1:28 ` Jens Axboe
2022-05-23 1:50 ` Jens Axboe
2022-05-23 2:43 ` Jens Axboe
2022-05-23 14:22 ` Al Viro
2022-05-23 14:34 ` Jens Axboe
2022-05-23 14:47 ` Al Viro
2022-05-23 15:12 ` Jens Axboe [this message]
2022-05-23 15:44 ` Jens Axboe
2022-05-23 15:49 ` Matthew Wilcox
2022-05-23 15:55 ` Jens Axboe
2022-05-23 16:03 ` Jens Axboe
2022-05-26 14:46 ` Jason A. Donenfeld
2022-05-27 10:09 ` Ingo Molnar
2022-05-27 10:15 ` Jason A. Donenfeld
2022-05-27 14:45 ` Samuel Neves
2022-05-27 10:25 ` Ingo Molnar
2022-05-27 10:36 ` Borislav Petkov
2022-05-28 20:54 ` Sedat Dilek
2022-05-28 20:38 ` Sedat Dilek
2022-05-28 20:39 ` Sedat Dilek
2022-05-23 16:15 ` Al Viro
2022-05-25 14:34 ` Matthew Wilcox
2022-05-26 23:19 ` Al Viro
2022-05-27 14:51 ` Jens Axboe
2022-05-22 12:21 ` Al Viro
2022-05-22 7:43 ` Christoph Hellwig
2022-05-22 12:41 ` Al Viro
2022-05-22 12:51 ` Christoph Hellwig
2021-06-21 14:22 ` Al Viro
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