linux-kernel - Re: [RFC 4/9] Atomic reclaim: Save irq flags in vmscan.c

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Message-ID: <p73vebhnauo.fsf@bingen.suse.de>
Date:	14 Aug 2007 22:02:23 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Christoph Lameter <clameter@....com>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC 4/9] Atomic reclaim: Save irq flags in vmscan.c

Christoph Lameter <clameter@....com> writes:

> Reclaim can be called with interrupts disabled in atomic reclaim.
> vmscan.c is currently using spinlock_irq(). Switch to spin_lock_irqsave().

I like the idea in principle. If this fully works out we could
potentially keep less memory free by default which would be a good
thing in general: free memory is bad memory.

But would be interesting to measure what the lock
changes do to interrupt latency. Probably nothing good.

A more benign alternative might be to just set a per CPU flag during
these critical sections and then only do atomic reclaim on a local
interrupt when the flag is not set.  That would make it a little less
reliable, but much less intrusive and with some luck still give many
of the benefits.

-Andi
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