From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-la0-f46.google.com (mail-la0-f46.google.com [209.85.215.46]) by kanga.kvack.org (Postfix) with ESMTP id 787546B0032 for ; Mon, 20 Apr 2015 18:03:01 -0400 (EDT) Received: by layy10 with SMTP id y10so137553140lay.0 for ; Mon, 20 Apr 2015 15:03:00 -0700 (PDT) Received: from mail-la0-x231.google.com (mail-la0-x231.google.com. [2a00:1450:4010:c03::231]) by mx.google.com with ESMTPS id a1si15903826lae.45.2015.04.20.15.02.59 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 20 Apr 2015 15:02:59 -0700 (PDT) Received: by laat2 with SMTP id t2so137569632laa.1 for ; Mon, 20 Apr 2015 15:02:58 -0700 (PDT) From: Rasmus Villemoes Subject: mempolicy ref-counting question Date: Tue, 21 Apr 2015 00:02:56 +0200 Message-ID: <87pp6y31bj.fsf@rasmusvillemoes.dk> MIME-Version: 1.0 Content-Type: text/plain Sender: owner-linux-mm@kvack.org List-ID: To: linux-mm@kvack.org Cc: Oleg Nesterov , Andrew Morton I'm trying to understand why "git grep mpol_get" doesn't give more hits than it does. Two of the users (kernel/sched/debug.c and fs/proc/task_mmu.c) seem to only hold the extra reference while writing to a seq_file. That leaves just three actual users. In particular, I'm wondering why __split_vma (and copy_vma) use vma_dup_policy instead of simply getting an extra reference on the old. I see there's some cpuset_being_rebound dance in mpol_dup, but I don't understand why that's needed: In __split_vma, we're holding mmap_sem, so either update_tasks_nodemask has already visited this mm via mpol_rebind_mm (which also takes the mmap_sem), so the old vma is already rebound, or the mpol_rebind_mm call will come later and rebind the mempolicy of both the old and new vma - why would it matter that the new vma's policy is rebound immediately? I'd appreciate it if someone could enlighten me (I'm probably missing something obvious). Rasmus -- 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