On Tue, 18 Jul 2006 18:03:54 +0800, yunfeng zhang said: > 2. Read-ahead process during page-in/out (page fault or swap out) should be > based on its VMA to enhance IO efficiency instead of the relative physical pages > in swap space. But wouldn't that end up causing a seek storm, rather than handling the pages in the order that minimizes the total seek distance, no matter where they are in memory? Remember - if you have a 2Ghz processor, and a disk that seeks in 1 millisecond, every seek is (*very* roughly) about 2 million instructions. So if we can burn 20 thousand instructions finding a read order that eliminates *one* seek, we're 1.98M instructions ahead. Now, if you have an improved read-ahead that spews out page requests that are both elevator-friendly and temporal-friendly, *then* you might be onto something. For instance, if you can identify 80 pages that will likely be needed in the next 50 milliseconds, of which 50 pages will be likely needed in the next 30ms, you want to issue those 50 first, in an elevator-friendly manner (uncaffienated handwave here) - and then issue the other 30 page requests in a second burst the next time the elevator goes by. Note this requires the read-ahead to get a *lot* more chummy with the elevator than it seems to currently. In particular, readahead would need to need to be able to hold off submitting the "later" 30 pages until it could be sure that the elevator wouldn't merge them into the queue in a way that would slow down the first 50 requests. If it does that already, somebody just smack me. And if there's a good reason not to do that, hand me some caffeine and a clue. :)
Attachment:
pgp2fbYrwqtPv.pgp
Description: PGP signature
- Follow-Ups:
- Re: Improvement on memory subsystem
- From: Ian Stirling <[email protected]>
- Re: Improvement on memory subsystem
- From: "yunfeng zhang" <[email protected]>
- Re: Improvement on memory subsystem
- References:
- Improvement on memory subsystem
- From: "yunfeng zhang" <[email protected]>
- Improvement on memory subsystem
- Prev by Date: Re: [PATCH] mm: inactive-clean list
- Next by Date: Re: input/eventX permissions, force feedback
- Previous by thread: Improvement on memory subsystem
- Next by thread: Re: Improvement on memory subsystem
- Index(es):
 |