From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from today.toronto.redhat.com (today.toronto.redhat.com [172.16.14.234]) by devserv.devel.redhat.com (8.11.0/8.11.0) with ESMTP id f1QNkOn01064 for ; Mon, 26 Feb 2001 18:46:24 -0500 Date: Mon, 26 Feb 2001 18:46:24 -0500 (EST) From: Ben LaHaise Subject: 2.5 page cache improvement idea Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org Return-Path: To: linux-mm@kvack.org List-ID: Hey folks, Here's an idea I just bounced off of Rik that seems like it would be pretty useful. Currently the page cache hash is system wide. For 2.5, I'm suggesting that we make the page cache hash a per-inode structure and possibly move the page index and mapping into the structure's information. Also, for dealing with hash collisions (which are going to happen under certain well known circumstances), we could move to a b*tree structure hanging off of the hashes. So we'd have a data structure that looks like the following: inode -> hash table -> struct page, index, mapping -> head of b*tree for overflow page -> pointer back to hash bucket/b*tree entry These changes would replace ~20 bytes in struct page with one pointer. Now, continuing along with making struct page smaller, we can blast away the wait queue and replace it with either a tiny-waitqueue (4 bytes) or make use of hashed wait queues (0 bytes per page). That would save another 8-12 bytes. Now, add in a couple of additional space savers like making the zone pointer an index, and eliminating the virtual pointer, and we have a struct page that's less than 32 bytes (we could even leave the index/mapping in that way). Tiny waitqueues are an idea based on the fact that we never have more than ~65536 waiters in the system (typically much less -> ~# of tasks). They replace the whole spinlock/next/prev structure with a single long that contains the index of the wait structure in a table in the high and low words. By making use of cmpxchg on x86, one doesn't need spinlocks to update this structure. These are just a couple of quick ideas that I'll try to implement at some point... Let me know of any thoughts on the matter. -ben -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux.eu.org/Linux-MM/