From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qk0-f197.google.com (mail-qk0-f197.google.com [209.85.220.197]) by kanga.kvack.org (Postfix) with ESMTP id 372986B02C4 for ; Wed, 17 May 2017 11:51:16 -0400 (EDT) Received: by mail-qk0-f197.google.com with SMTP id k74so5900428qke.4 for ; Wed, 17 May 2017 08:51:16 -0700 (PDT) Received: from userp1040.oracle.com (userp1040.oracle.com. [156.151.31.81]) by mx.google.com with ESMTPS id e23si2554128qte.304.2017.05.17.08.51.15 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 17 May 2017 08:51:15 -0700 (PDT) Subject: Re: [PATCH v3 4/4] mm: Adaptive hash table scaling References: <1488432825-92126-1-git-send-email-pasha.tatashin@oracle.com> <1488432825-92126-5-git-send-email-pasha.tatashin@oracle.com> <20170303153247.f16a31c95404c02a8f3e2c5f@linux-foundation.org> From: Pasha Tatashin Message-ID: Date: Wed, 17 May 2017 11:51:06 -0400 MIME-Version: 1.0 In-Reply-To: <20170303153247.f16a31c95404c02a8f3e2c5f@linux-foundation.org> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton , Michal Hocko Cc: linux-mm@kvack.org, sparclinux@vger.kernel.org, linux-fsdevel@vger.kernel.org, Al Viro On 03/03/2017 06:32 PM, Andrew Morton wrote: > On Thu, 2 Mar 2017 00:33:45 -0500 Pavel Tatashin wrote: > >> Allow hash tables to scale with memory but at slower pace, when HASH_ADAPT >> is provided every time memory quadruples the sizes of hash tables will only >> double instead of quadrupling as well. This algorithm starts working only >> when memory size reaches a certain point, currently set to 64G. >> >> This is example of dentry hash table size, before and after four various >> memory configurations: >> >> MEMORY SCALE HASH_SIZE >> old new old new >> 8G 13 13 8M 8M >> 16G 13 13 16M 16M >> 32G 13 13 32M 32M >> 64G 13 13 64M 64M >> 128G 13 14 128M 64M >> 256G 13 14 256M 128M >> 512G 13 15 512M 128M >> 1024G 13 15 1024M 256M >> 2048G 13 16 2048M 256M >> 4096G 13 16 4096M 512M >> 8192G 13 17 8192M 512M >> 16384G 13 17 16384M 1024M >> 32768G 13 18 32768M 1024M >> 65536G 13 18 65536M 2048M > > OK, but what are the runtime effects? Presumably some workloads will > slow down a bit. How much? How do we know that this is a worthwhile > tradeoff? > > If the effect of this change is "undetectable" then those hash tables > are simply too large, and additional tuning is needed, yes? > Hi Andrew, The effect of this change on runtime is undetectable as filesystem growth is not proportional to machine memory size as what is currently assumed. The change effects only large memory machine. Additional tuning might be needed, but that can be done by the clients of the kmem_cache_create interface, not the generic cache allocator itself. Thank you, Pasha -- 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