Re: [PATCH] mm: limit lowmem_reserve

From: Nick Piggin
Date: Thu May 18 2006 - 03:25:32 EST

Con Kolivas wrote:
On Thursday 18 May 2006 17:11, Nick Piggin wrote:

If we're under memory pressure, kswapd will try to free up any candidate
zone, yes.

On my test case this indeed happens and my ZONE_DMA never goes below 3000
pages free. If I lower the reserve even further my pages free gets stuck
at 3208 and can't free any more, and doesn't ever drop below that either.

Here is the patch I was proposing

What problem does that fix though?

It's a generic concern and I honestly don't know how significant it is which is why I'm asking if it needs attention. That concern being that any time we're under any sort of memory pressure, ZONE_DMA will undergo intense reclaim even though there may not really be anything specifically going on in ZONE_DMA. It just seems a waste of cycles doing that.

If it doesn't have any/much pagecache or slab cache in it, there won't be
intense reclaim; if it does then it can be reclaimed and the memory used.

reclaim / allocation could be slightly smarter about scaling watermarks,
however I don't think it is much of an issue at the moment.

SUSE Labs, Novell Inc.
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