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From: Nadav Amit <[email protected]>
To: [email protected]
Cc: Jens Axboe <[email protected]>,
	Andrea Arcangeli <[email protected]>,
	Peter Xu <[email protected]>,
	Alexander Viro <[email protected]>,
	[email protected], [email protected],
	[email protected]
Subject: Re: [RFC PATCH 11/13] fs/userfaultfd: complete write asynchronously
Date: Tue, 1 Dec 2020 23:12:42 -0800	[thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>

> On Nov 28, 2020, at 4:45 PM, Nadav Amit <[email protected]> wrote:
> 
> From: Nadav Amit <[email protected]>
> 
> Userfaultfd writes can now be used for copy/zeroing. When using iouring
> with userfaultfd, performing the copying/zeroing on the faulting thread
> instead of the handler/iouring thread has several advantages:
> 
> (1) The data of the faulting thread will be available on the local
> caches, which would make subsequent memory accesses faster.
> 
> (2) find_vma() would be able to use the vma-cache, which cannot be done
> from a different process or io-uring kernel thread.
> 
> (3) The page is more likely to be allocated on the correct NUMA node.
> 
> To do so, userfaultfd work queue structs are extended to hold the
> information that is required for the faulting thread to copy/zero. The
> handler wakes one of the faulting threads to perform the copy/zero and
> that thread wakes the other threads after the zero/copy is done.

I noticed some bugs of mine in this patch, but more importantly I realized
that the there may be a more performant solution to do the copying on the
faulting thread - without async-writes.

Please do not review this patch and the next one (12/13).

Feedback for the rest of the series is of course welcomed.

Regards,
Nadav

  reply	other threads:[~2020-12-02  7:13 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-11-29  0:45 [RFC PATCH 00/13] fs/userfaultfd: support iouring and polling Nadav Amit
2020-11-29  0:45 ` [RFC PATCH 01/13] fs/userfaultfd: fix wrong error code on WP & !VM_MAYWRITE Nadav Amit
2020-12-01 21:22   ` Mike Kravetz
2020-12-21 19:01     ` Peter Xu
2020-11-29  0:45 ` [RFC PATCH 02/13] fs/userfaultfd: fix wrong file usage with iouring Nadav Amit
2020-11-29  0:45 ` [RFC PATCH 03/13] selftests/vm/userfaultfd: wake after copy failure Nadav Amit
2020-12-21 19:28   ` Peter Xu
2020-12-21 19:51     ` Nadav Amit
2020-12-21 20:52       ` Peter Xu
2020-12-21 20:54         ` Nadav Amit
2020-11-29  0:45 ` [RFC PATCH 04/13] fs/userfaultfd: simplify locks in userfaultfd_ctx_read Nadav Amit
2020-11-29  0:45 ` [RFC PATCH 05/13] fs/userfaultfd: introduce UFFD_FEATURE_POLL Nadav Amit
2020-11-29  0:45 ` [RFC PATCH 06/13] iov_iter: support atomic copy_page_from_iter_iovec() Nadav Amit
2020-11-29  0:45 ` [RFC PATCH 07/13] fs/userfaultfd: support read_iter to use io_uring Nadav Amit
2020-11-30 18:20   ` Jens Axboe
2020-11-30 19:23     ` Nadav Amit
2020-11-29  0:45 ` [RFC PATCH 08/13] fs/userfaultfd: complete reads asynchronously Nadav Amit
2020-11-29  0:45 ` [RFC PATCH 09/13] fs/userfaultfd: use iov_iter for copy/zero Nadav Amit
2020-11-29  0:45 ` [RFC PATCH 10/13] fs/userfaultfd: add write_iter() interface Nadav Amit
2020-11-29  0:45 ` [RFC PATCH 11/13] fs/userfaultfd: complete write asynchronously Nadav Amit
2020-12-02  7:12   ` Nadav Amit [this message]
2020-11-29  0:45 ` [RFC PATCH 12/13] fs/userfaultfd: kmem-cache for wait-queue objects Nadav Amit
2020-11-30 19:51   ` Nadav Amit
2020-11-29  0:45 ` [RFC PATCH 13/13] selftests/vm/userfaultfd: iouring and polling tests Nadav Amit

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