From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from nautica.notk.org ([91.121.71.147]:44673 "EHLO nautica.notk.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727667AbeGLOuT (ORCPT ); Thu, 12 Jul 2018 10:50:19 -0400 Date: Thu, 12 Jul 2018 16:40:12 +0200 From: Dominique Martinet To: Greg Kurz Cc: Matthew Wilcox , Latchesar Ionkov , Eric Van Hensbergen , linux-kernel@vger.kernel.org, Ron Minnich , linux-fsdevel@vger.kernel.org, v9fs-developer@lists.sourceforge.net Subject: Re: [V9fs-developer] [PATCH v2 4/6] 9p: Embed wait_queue_head into p9_req_t Message-ID: <20180712144012.GA21574@nautica> References: <20180711210225.19730-1-willy@infradead.org> <20180711210225.19730-5-willy@infradead.org> <20180712163649.36057b6e@bahia.lan> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20180712163649.36057b6e@bahia.lan> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: Greg Kurz wrote on Thu, Jul 12, 2018: > This is true when all tags have been used at least once. But the current code > lazily allocates the wait_queue_head_t, ie, only when a tag is used for the > first time. Your patch causes a full row of wait_quest_head_t to be pre-allocated. > > ie, P9_ROW_MAXTAG * 24 = 255 * 24 = 6120 > > instead of (P9_ROW_MAXTAG * 8) + 24 = 255 * 8 + 24 = 2064 > > This is nearly a page of allocated memory that might be never used. > > Not sure if this is a problem though... I thought the exact same, but the next patch in the serie removes that array and allocates even more lazily with a slab, so this was a no-brainer :) -- Dominique Martinet