Messages in this thread | | | Date | Mon, 21 Jul 2008 22:36:09 -0400 | From | Rik van Riel <> | Subject | Re: [PATCH -mm] mm: more likely reclaim MADV_SEQUENTIAL mappings |
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On Tue, 22 Jul 2008 12:02:26 +1000 Nick Piggin <nickpiggin@yahoo.com.au> wrote:
> I don't actually care what the man page or posix says if it is obviously > silly behaviour. If you want to dispute the technical points of my post, > that would be helpful.
Application writers read the man page and expect MADV_SEQUENTIAL to do roughly what the name and description imply.
If you think that the kernel should not bother implementing what the application writers expect, and the application writers should implement special drop-behind magic for Linux, your expectations may not be entirely realistic.
> Consider this: if the app already has dedicated knowledge and > syscalls to know about this big sequential copy, then it should > go about doing it the *right* way and really get performance > improvement. Automatic unmap-behind even if it was perfect still > needs to scan LRU lists to reclaim.
Doing nothing _also_ ends up with the kernel scanning the LRU lists, once memory fills up.
Scanning the LRU lists is a given.
All that the patch by Johannes does is make sure the kernel does the right thing when it runs into an MADV_SEQUENTIAL page on the inactive_file list: evict the page immediately, instead of having it pass through the active list and the inactive list again.
This reduces the number of times that MADV_SEQUENTIAL pages get scanned from 3 to 1, while protecting the working set from MADV_SEQUENTIAL pages.
-- All rights reversed.
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