Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756231Ab1FETQU (ORCPT ); Sun, 5 Jun 2011 15:16:20 -0400 Received: from smtp-out.google.com ([216.239.44.51]:6351 "EHLO smtp-out.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753870Ab1FETQT (ORCPT ); Sun, 5 Jun 2011 15:16:19 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=google.com; s=beta; h=date:from:x-x-sender:to:cc:subject:in-reply-to:message-id :references:user-agent:mime-version:content-type; b=RBD+MvYP5hoKfDbFuIaMXva5oG9gtPZC9iy8+gHV5OInxc5qF+QMX/c0ggizqdHVVb g1DPkMcQBjm5W0DuGggQ== Date: Sun, 5 Jun 2011 12:16:08 -0700 (PDT) From: Hugh Dickins X-X-Sender: hugh@sister.anvils To: Al Viro cc: linux-mm@kvack.org, Mel Gorman , linux-kernel@vger.kernel.org Subject: Re: ENOSPC returned by handle_mm_fault() In-Reply-To: <20110605134317.GF11521@ZenIV.linux.org.uk> Message-ID: References: <20110605134317.GF11521@ZenIV.linux.org.uk> User-Agent: Alpine 2.00 (LSU 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-System-Of-Record: true Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2159 Lines: 47 On Sun, 5 Jun 2011, Al Viro wrote: > When alloc_huge_page() runs afoul of quota, it returns ERR_PTR(-ENOSPC). > Callers do not expect that - hugetlb_cow() returns ENOSPC if it gets that > and so does hugetlb_no_page(). Eventually the thing propagates back to > hugetlb_fault() and is returned by it. > > Callers of hugetlb_fault() clearly expect a bitmap of VM_... and > not something from errno.h: one place is > ret = hugetlb_fault(mm, vma, vaddr, > (flags & FOLL_WRITE) ? FAULT_FLAG_WRITE : 0); > spin_lock(&mm->page_table_lock); > if (!(ret & VM_FAULT_ERROR)) > continue; > and another is handle_mm_fault(), which ends up returning ENOSPC and *its* > callers are definitely not ready to deal with that. > > ENOSPC is 28, i.e. VM_FAULT_MAJOR | VM_FAULT_WRITE | VM_FAULT_HWPOISON; > it's also theoretically possible to get ENOMEM if region_chg() ends up > hitting > nrg = kmalloc(sizeof(*nrg), GFP_KERNEL); > if (!nrg) > return -ENOMEM; > region_chg() <- vma_needs_reservation() <- alloc_huge_page() and from that > point as with ENOSPC. ENOMEM is 12, i.e. VM_FAULT_MAJOR | VM_FAULT_WRITE... Good find, news to me. Interesting uses of -PTR_ERR()! Looks like we'd better not have more than 12 VM_FAULT_ flags. > > Am I right assuming that we want VM_FAULT_OOM in both cases? No, where hugetlb_get_quota() fails it should be VM_FAULT_SIGBUS: there's no excuse to go on an OOM-killing spree just because hugetlb quota is exhausted. VM_FAULT_OOM is appropriate where vma_needs_reservation() fails, because region_chg() couldn't kmalloc a structure, as you point out. (Though that doesn't matter much, since the only way the kmalloc can fail is when this task is already selected for OOM-kill - I think.) Hugh -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/