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Date: Mon, 26 Nov 2001 11:29:19 -0800
From: Andrew Morton <akpm@zip.com.au>
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To: "David S. Miller" <davem@redhat.com>
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Subject: Re: [PATCH] Scalable page cache
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"David S. Miller" wrote:
> 
>    From: Ingo Molnar <mingo@elte.hu>
>    Date: Mon, 26 Nov 2001 21:29:39 +0100 (CET)
> 
>    so i'm not against removing (or improving) the hash [our patch in fact
>    just left the hash alone], but the patch presented is not a win IMO.
> 
> Maybe you should give it a test to find out for sure :)

umm..  I've never seen any numbers from you, David.

Correct me if I'm wrong, but the pagecache_hash cost is
significant in the following situations:

1: TUX, because its pagecache lookups are not associated with
   a page copy.  This copy makes the benefits of the patch
   unmeasurable with other workloads.

1a: Other sendfile-intensive applications. (Theoretical benefit.
    No benchmark results have been seen).

2: NUMA hardware, where the cost of cacheline transfer is much
   higher.

ergo, there is no point in futzing with the pagecache_lock *at all*
until either TUX is merged, or we decide to support large-scale
NUMA hardware well, which will require changes in other places.

Prove me wrong.  Please.

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