From: Johannes Weiner <hannes@cmpxchg.org>
To: Christoph Hellwig <hch@infradead.org>
Cc: Pavel Begunkov <asml.silence@gmail.com>,
Jens Axboe <axboe@kernel.dk>,
Alexander Viro <viro@zeniv.linux.org.uk>,
linux-fsdevel@vger.kernel.org, io-uring@vger.kernel.org,
linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
Matthew Wilcox <willy@infradead.org>
Subject: Re: [PATCH 2/2] block: no-copy bvec for direct IO
Date: Fri, 11 Dec 2020 15:06:22 +0100 [thread overview]
Message-ID: <20201211140622.GA286014@cmpxchg.org> (raw)
In-Reply-To: <20201209084005.GC21968@infradead.org>
On Wed, Dec 09, 2020 at 08:40:05AM +0000, Christoph Hellwig wrote:
> > + /*
> > + * In practice groups of pages tend to be accessed/reclaimed/refaulted
> > + * together. To not go over bvec for those who didn't set BIO_WORKINGSET
> > + * approximate it by looking at the first page and inducing it to the
> > + * whole bio
> > + */
> > + if (unlikely(PageWorkingset(iter->bvec->bv_page)))
> > + bio_set_flag(bio, BIO_WORKINGSET);
>
> IIRC the feedback was that we do not need to deal with BIO_WORKINGSET
> at all for direct I/O.
Yes, this hunk is incorrect. We must not use this flag for direct IO.
It's only for paging IO, when you bring in the data at page->mapping +
page->index. Otherwise you tell the pressure accounting code that you
are paging in a thrashing page, when really you're just reading new
data into a page frame that happens to be hot.
(As per the other thread, bio_add_page() currently makes that same
mistake for direct IO. I'm fixing that.)
next prev parent reply other threads:[~2020-12-12 1:00 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-09 2:19 [RFC 0/2] nocopy bvec for direct IO Pavel Begunkov
2020-12-09 2:19 ` [PATCH 1/2] iov: introduce ITER_BVEC_FLAG_FIXED Pavel Begunkov
2020-12-09 8:36 ` Christoph Hellwig
2020-12-09 9:06 ` Christoph Hellwig
2020-12-09 11:54 ` Pavel Begunkov
2020-12-09 13:07 ` Al Viro
2020-12-09 13:37 ` Pavel Begunkov
2020-12-09 17:55 ` Christoph Hellwig
2020-12-09 18:24 ` Matthew Wilcox
2020-12-13 22:09 ` Pavel Begunkov
2020-12-09 2:19 ` [PATCH 2/2] block: no-copy bvec for direct IO Pavel Begunkov
2020-12-09 8:40 ` Christoph Hellwig
2020-12-09 12:01 ` Pavel Begunkov
2020-12-09 12:05 ` Christoph Hellwig
2020-12-09 12:03 ` Pavel Begunkov
2020-12-11 14:06 ` Johannes Weiner [this message]
2020-12-11 14:20 ` Pavel Begunkov
2020-12-11 15:38 ` Johannes Weiner
2020-12-11 15:47 ` Pavel Begunkov
2020-12-11 16:13 ` Johannes Weiner
2020-12-09 21:13 ` David Laight
2020-12-09 6:50 ` [RFC 0/2] nocopy " Christoph Hellwig
2020-12-09 11:54 ` Pavel Begunkov
2020-12-09 16:53 ` Jens Axboe
2020-12-13 22:03 ` Pavel Begunkov
2020-12-09 17:06 ` Al Viro
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