From: David Howells <dhowells@redhat.com>
To: Matthew Wilcox <willy@infradead.org>,
Mike Marshall <hubcap@omnibond.com>
Cc: dhowells@redhat.com, linux-fsdevel <linux-fsdevel@vger.kernel.org>
Subject: Re: [RFC PATCH v2] implement orangefs_readahead
Date: Sat, 27 Mar 2021 08:31:38 +0000 [thread overview]
Message-ID: <1507388.1616833898@warthog.procyon.org.uk> (raw)
In-Reply-To: <20210327035019.GG1719932@casper.infradead.org>
Matthew Wilcox <willy@infradead.org> wrote:
> > 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!
Yeah... The cleanup function that I posted potentially happens asynchronously
from the ->readahead function, so the ractl consumption has to be done
elsewhere and may already have happened. In the case of the code I posted
from, it's actually done in the netfs lib that's in the works:
void netfs_readahead(...)
{
...
/* Drop the refs on the pages here rather than in the cache or
* filesystem. The locks will be dropped in netfs_rreq_unlock().
*/
while ((page = readahead_page(ractl)))
put_page(page);
...
}
> 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.
I'm not sure either is useful for my case since iov_iter_xarray() for me isn't
being used anywhere that there's an ractl and I still have to drop the page
refs.
However, in Mike's orangefs_readahead_cleanup(), he could replace:
rcu_read_lock();
xas_for_each(&xas, page, last) {
page_endio(page, false, 0);
put_page(page);
}
rcu_read_unlock();
with:
while ((page = readahead_page(ractl))) {
page_endio(page, false, 0);
put_page(page);
}
maybe?
David
next prev parent reply other threads:[~2021-03-27 8:32 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
2021-03-27 8:31 ` David Howells [this message]
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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