Nick Piggin wrote:
Eric St-Laurent wrote:
On Wed, 2007-25-07 at 15:19 +1000, Nick Piggin wrote:
What *I* think is supposed to happen is that newly read in pages get
put on the inactive list, and unless they get accessed againbefore
being reclaimed, they are allowed to fall off the end of the list
without disturbing active data too much.
I think there is a missing piece here, that we used to ease the reclaim
pressure off the active list when the inactive list grows relatively
much larger than it (which could indicate a lot of use-once pages in
the system).
Maybe a new list should be added to put newly read pages in it. If they
are not used or used once after a certain period, they can be moved to
the inactive list (or whatever).
Newly read pages...
- ... not used after this period are excessive readahead, we discard
immediately.
- ... used only once after this period, we discard soon.
- ... used many/frequently are moved to active list.
Surely the scan rate (do I make sense?) should be different for this
newly-read list and the inactive list.
A new list could be a possibility. One problem with adding lists is just
trying to work out how to balance scanning rates between them, another
problem is CPU overhead of moving pages from one to another... but don't
let me stop you if you want to jump in and try something :)
I also remember your split mapped/unmapped active list patches from a
while ago.
Can someone point me to a up-to-date documentation about the Linux VM?
The books and documents I've seen are outdated.
If you just want to play with page reclaim algorithms, try reading over
mm/vmscan.c. If you don't know much about the Linux VM internals before,
don't worry too much about the fine details and start by getting an idea
of how pages move between the active and inactive lists.
I've got a nice list of problems with the VM at
http://linux-mm.org/PageoutFailureModes :)
I should post my latest version of the split LRU
lists code. I'm still working on SEQ replacement
for the anonymous pages...
OK here is one which just changes the rate that the active and inactive
lists get scanned. Data corruption bugs should be minimal ;)
I had something like that in mind for the file
pages. I am a bit nervous about introducing
such a change while file and anonymous pages
share the same LRU, though...
--
Politics is the struggle between those who want to make their country
the best in the world, and those who believe it already is. Each group
calls the other unpatriotic.
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