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From: Johannes Weiner <[email protected]>
To: Pavel Begunkov <[email protected]>
Cc: Christoph Hellwig <[email protected]>,
	Jens Axboe <[email protected]>,
	Alexander Viro <[email protected]>,
	[email protected], [email protected],
	[email protected], [email protected],
	Matthew Wilcox <[email protected]>
Subject: Re: [PATCH 2/2] block: no-copy bvec for direct IO
Date: Fri, 11 Dec 2020 16:38:36 +0100	[thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>

On Fri, Dec 11, 2020 at 02:20:11PM +0000, Pavel Begunkov wrote:
> On 11/12/2020 14:06, Johannes Weiner wrote:
> > 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.)
> 
> I have that stuff fixed, it just didn't go into the RFC. That's basically
> removing replacing add_page() with its version without BIO_WORKINGSET
> in bio_iov_iter_get_pages() and all __bio_iov_*_{add,get}_pages() +
> fix up ./fs/direct-io.c. Should cover all direct cases if I didn't miss
> some.

Ah, that's fantastic! Thanks for clarifying.

  reply	other threads:[~2020-12-11 16:37 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
2020-12-11 14:20       ` Pavel Begunkov
2020-12-11 15:38         ` Johannes Weiner [this message]
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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