Re: [PATCH][0/8] (Targeting 2.6.17) Posix memory locking and balancedmlock-LRU semantic

From: Nick Piggin
Date: Tue Mar 21 2006 - 07:52:48 EST

Stone Wang wrote:
Both one of my friends(who is working on a DBMS oriented from
PostgreSQL) and i had encountered unexpected OOMs with mlock/mlockall.

I'm not sure this is a great idea. There are more conditions than just
mlock that prevent pages being reclaimed. Running out of swap, for
example, no swap, page temporarily pinned (in other words -- any duration
from fleeting to permanent). I think something _much_ simpler could be
done for a more general approach just to teach the VM to tolerate these
pages a bit better.

Also, supposing we do want this, I think there is a fairly significant
queue of mm stuff you need to line up behind... it is probably asking
too much to target 2.6.17 for such a significant change in any case.

But despite all that I looked though and have a few comments ;)
Kudos for jumping in and getting your hands dirty! It can be tricky code.

The patch brings Linux with:
1. Posix mlock/munlock/mlockall/munlockall.
Get mlock/munlock/mlockall/munlockall to Posix definiton: transaction-like,
just as described in the manpage(2) of mlock/munlock/mlockall/munlockall.
Thus users of mlock system call series will always have an clear map of
mlocked areas.

In what way are we not now posix compliant now?

SUSE Labs, Novell Inc.

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