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To: <mingo@elte.hu>
Cc: Anton Blanchard <anton@samba.org>, Linus Torvalds <torvalds@transmeta.com>,
        Andrea Arcangeli <andrea@suse.de>,
        Rik van Riel <riel@conectiva.com.br>, John Stoffel <stoffel@casc.com>,
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Subject: Re: [PATCH] Radix-tree pagecache for 2.5
In-Reply-To: <Pine.LNX.4.33.0202011801260.11284-100000@localhost.localdomain>
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From: Momchil Velikov <velco@fadata.bg>
In-Reply-To: <Pine.LNX.4.33.0202011801260.11284-100000@localhost.localdomain>
Date: 01 Feb 2002 17:26:42 +0200
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>>>>> "Ingo" == Ingo Molnar <mingo@elte.hu> writes:

Ingo> On 1 Feb 2002, Momchil Velikov wrote:

Ingo> files are used. With one big file (or a few big files), the i_shared_lock
Ingo> will always bounce between CPUs wildly in read() workloads, degrading
>> 
>> Will there be difference between bounces of a rwlock in the radix tree
>> variant and the cache misses in hashed locks variant for the case of
>> concurrently accessed large file ?

Ingo> definitely, because in the case of page buckets there are many locks
Ingo> hashed in a mapping-neutral way. Ie. different parts of the same file will
Ingo> likely map to different spinlocks.

That's why it's likely to miss on each access.  

Ingo> In the radix tree case all pages in the inode will map to the
Ingo> same spinlock.

That's why it's likely to bounce on each access.

So, is there any difference ? :)

Regards,
-velco
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