From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qt0-f200.google.com (mail-qt0-f200.google.com [209.85.216.200]) by kanga.kvack.org (Postfix) with ESMTP id 075F06B0005 for ; Wed, 30 May 2018 02:12:11 -0400 (EDT) Received: by mail-qt0-f200.google.com with SMTP id p12-v6so7831551qtg.5 for ; Tue, 29 May 2018 23:12:11 -0700 (PDT) Received: from mail-sor-f73.google.com (mail-sor-f73.google.com. [209.85.220.73]) by mx.google.com with SMTPS id b18-v6sor22141665qtp.130.2018.05.29.23.12.10 for (Google Transport Security); Tue, 29 May 2018 23:12:10 -0700 (PDT) Date: Tue, 29 May 2018 23:12:07 -0700 In-Reply-To: <20180529025722.GA25784@bombadil.infradead.org> Message-Id: Mime-Version: 1.0 References: <20180529024025.58353-1-gthelen@google.com> <20180529025722.GA25784@bombadil.infradead.org> Subject: Re: [PATCH] mm: convert scan_control.priority int => byte From: Greg Thelen Content-Type: text/plain; charset="UTF-8" Sender: owner-linux-mm@kvack.org List-ID: To: Matthew Wilcox Cc: Andrew Morton , Michal Hocko , Johannes Weiner , linux-mm@kvack.org, linux-kernel@vger.kernel.org Matthew Wilcox wrote: > On Mon, May 28, 2018 at 07:40:25PM -0700, Greg Thelen wrote: >> Reclaim priorities range from 0..12(DEF_PRIORITY). >> scan_control.priority is a 4 byte int, which is overkill. >> >> Since commit 6538b8ea886e ("x86_64: expand kernel stack to 16K") x86_64 >> stack overflows are not an issue. But it's inefficient to use 4 bytes >> for priority. > > If you're looking to shave a few more bytes, allocation order can fit > in a u8 too (can't be more than 6 bits, and realistically won't be more > than 4 bits). reclaim_idx likewise will fit in a u8, and actually won't > be more than 3 bits. Nod. Good tip. Included in ("[PATCH v2] mm: condense scan_control"). > I am sceptical that nr_to_reclaim should really be an unsigned long; I > don't think we should be trying to free 4 billion pages in a single call. > nr_scanned might be over 4 billion (!) but nr_reclaimed can probably > shrink to unsigned int along with nr_to_reclaim. Agreed. For patch simplicity, I'll pass on this for now.