From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <464F44BD.3040209@cosmosbay.com> Date: Sat, 19 May 2007 20:41:01 +0200 From: Eric Dumazet MIME-Version: 1.0 Subject: Re: [PATCH] MM : alloc_large_system_hash() can free some memory for non power-of-two bucketsize References: <20070518115454.d3e32f4d.dada1@cosmosbay.com> <20070519182123.GD19966@holomorphy.com> In-Reply-To: <20070519182123.GD19966@holomorphy.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 8bit Sender: owner-linux-mm@kvack.org Return-Path: To: William Lee Irwin III Cc: Andrew Morton , "linux-mm@kvack.org" , linux kernel , David Miller List-ID: William Lee Irwin III a ecrit : > On Fri, May 18, 2007 at 11:54:54AM +0200, Eric Dumazet wrote: >> alloc_large_system_hash() is called at boot time to allocate space >> for several large hash tables. >> Lately, TCP hash table was changed and its bucketsize is not a >> power-of-two anymore. >> On most setups, alloc_large_system_hash() allocates one big page >> (order > 0) with __get_free_pages(GFP_ATOMIC, order). This single >> high_order page has a power-of-two size, bigger than the needed size. >> We can free all pages that wont be used by the hash table. >> On a 1GB i386 machine, this patch saves 128 KB of LOWMEM memory. >> TCP established hash table entries: 32768 (order: 6, 393216 bytes) > > The proper way to do this is to convert the large system hashtable > users to use some data structure / algorithm other than hashing by > separate chaining. No thanks. This was already discussed to death on netdev. To date, hash tables are a good compromise. I dont mind losing part of memory, I prefer to keep good performance when handling 1.000.000 or more tcp sessions. -- 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-mm.org/ . Don't email: email@kvack.org