From: Matthew Wilcox <willy@infradead.org>
To: Mike Marshall <hubcap@omnibond.com>
Cc: David Howells <dhowells@redhat.com>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>
Subject: Re: [RFC PATCH v2] implement orangefs_readahead
Date: Sat, 27 Mar 2021 03:50:19 +0000 [thread overview]
Message-ID: <20210327035019.GG1719932@casper.infradead.org> (raw)
In-Reply-To: <CAOg9mSQMDzMfg3C0TUvTWU61zQdjnthXSy01mgY=CpgaDjj=Pw@mail.gmail.com>
On Fri, Mar 26, 2021 at 10:55:44PM -0400, Mike Marshall wrote:
> Hi David.
>
> I implemented a version with iov_iter_xarray (below).
> It appears to be doing "the right thing" when it
> gets called, but then I get a backtrace in the kernel
> ring buffer "RIP: 0010:read_pages+0x1a1/0x2c0" which is
> page dumped because: VM_BUG_ON_PAGE(!PageLocked(page))
> ------------[ cut here ]------------
> kernel BUG at include/linux/pagemap.h:892!
>
> So it seems that in mm/readahead.c/read_pages I end up
> entering the "Clean up the remaining pages" part, and
> never make it through even one iteration... it happens
> whether I use readahead_expand or not.
>
> I've been looking at it a long time :-), I'll look more
> tomorrow... do you see anything obvious?
Yes; Dave's sample code doesn't consume the pages from the readahead
iterator, so the core code thinks you didn't consume them and unlocks
/ puts the pages for you. That goes wrong, because you did actually
consume them. Glad I added the assertions now!
We should probably add something like:
static inline void readahead_consume(struct readahead_control *ractl,
unsigned int nr)
{
ractl->_nr_pages -= nr;
ractl->_index += nr;
}
to indicate that you consumed the pages other than by calling
readahead_page() or readahead_page_batch(). Or maybe Dave can
wrap iov_iter_xarray() in a readahead_iter() macro or something
that takes care of adjusting index & nr_pages for you.
next prev parent reply other threads:[~2021-03-27 3:51 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-31 22:25 [RFC PATCH] implement orangefs_readahead Mike Marshall
2021-02-01 13:08 ` Matthew Wilcox
2021-02-02 3:32 ` Mike Marshall
2021-03-13 15:31 ` [RFC PATCH v2] " Mike Marshall
2021-03-17 3:04 ` Mike Marshall
2021-03-24 11:10 ` David Howells
2021-03-27 2:55 ` Mike Marshall
2021-03-27 3:50 ` Matthew Wilcox [this message]
2021-03-27 8:31 ` David Howells
2021-03-27 13:56 ` Matthew Wilcox
2021-03-27 15:40 ` Mike Marshall
2021-03-27 15:56 ` Matthew Wilcox
2021-03-28 3:04 ` Mike Marshall
2021-03-29 1:51 ` Mike Marshall
2021-03-29 9:37 ` David Howells
2021-03-29 23:25 ` Mike Marshall
[not found] ` <3726695.1617284551@warthog.procyon.org.uk >
2021-04-13 15:08 ` David Howells
2021-04-16 14:36 ` Mike Marshall
2021-04-16 15:14 ` Matthew Wilcox
2021-04-25 1:51 ` Mike Marshall
2021-04-16 15:41 ` David Howells
2021-04-25 1:43 ` Mike Marshall
2021-04-25 7:49 ` David Howells
2021-04-26 14:53 ` Mike Marshall
2021-04-26 19:01 ` Mike Marshall
2021-04-26 20:01 ` David Howells
2021-04-26 8:37 ` David Howells
2021-04-01 13:42 ` David Howells
2021-04-08 20:39 ` Mike Marshall
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