From mboxrd@z Thu Jan 1 00:00:00 1970 From: Arne Jansen Subject: Re: [RFC] Tree fragmentation and prefetching Date: Fri, 25 Mar 2011 21:53:24 +0100 Message-ID: <4D8D00C4.9020005@gmx.net> References: <4D89F03A.9050306@gmx.net> <1300908672-sup-9552@think> <4D8CF7AB.4010102@gmx.net> <1301084093-sup-5455@think> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Cc: Linux Btrfs To: Chris Mason Return-path: In-Reply-To: <1301084093-sup-5455@think> List-ID: On 25.03.2011 21:15, Chris Mason wrote: > Excerpts from Arne Jansen's message of 2011-03-25 16:14:35 -0400: >> On 23.03.2011 20:32, Chris Mason wrote: >>> Excerpts from Arne Jansen's message of 2011-03-23 09:06:02 -0400: >>>> >>>> For the implementation I'd need an interface which I haven't been able >>>> to find yet. Currently I can trigger the read of several pages / tree >>>> blocks and wait for the completion of each of them. What I'd need would >>>> be an interface that gives me a callback on each completion or a waiting >>>> function that wakes up on each completion with the information which >>>> pages just completed. >>>> One way to achieve this would be to add a hook, but I gladly take any >>>> implementation hints. >>> >>> We have the bio endio call backs for this, I think that's the only thing >>> you can use. >>> >> >> ok, so I'll add a new extent state bit EXTENT_READAHEAD and test for it >> in btree_readpage_end_io_hook. > > It's also common to use a chain of endio handlers. If you're allocating > any state for the RA, you just save the original endio handler in your > new struct, and then use your own endio handler that does the readahead > smarts. > Do you mean replacing the bio end_io handler or the readpage_end_io_hook? As I want the pages to end up in the page cache, I'd like to use as much of the existing infrastructure as possible. To intercept the bio deep down in the chain would mean to duplicate some code on the way down and on the way up again. -Arne