From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758754Ab0LNAvx (ORCPT ); Mon, 13 Dec 2010 19:51:53 -0500 Received: from smtp-out.google.com ([216.239.44.51]:39965 "EHLO smtp-out.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758098Ab0LNAvw (ORCPT ); Mon, 13 Dec 2010 19:51:52 -0500 DomainKey-Signature: a=rsa-sha1; c=nofws; d=google.com; s=beta; h=date:from:to:cc:subject:message-id:references:mime-version :content-type:content-disposition:in-reply-to:user-agent; b=xEWfJygDLkIRLRtAaQgYVmkPzwlguar/NNMvTI4ZBJ+aMKwjMngoyY/NT81bCRb2mj DLK4cPxAycNbuYlwff6g== Date: Mon, 13 Dec 2010 16:51:40 -0800 From: Michel Lespinasse To: Andrew Morton , Linus Torvalds Cc: "linux-mm@kvack.org" , Hugh Dickins , Rik van Riel , Peter Zijlstra , Nick Piggin , KOSAKI Motohiro , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH 1/6] mlock: only hold mmap_sem in shared mode when faulting in pages Message-ID: <20101214005140.GA29904@google.com> References: <1291335412-16231-1-git-send-email-walken@google.com> <1291335412-16231-2-git-send-email-walken@google.com> <20101208152740.ac449c3d.akpm@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.20 (2009-06-14) X-System-Of-Record: true Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Dec 9, 2010 at 10:11 PM, Linus Torvalds wrote: > On Wednesday, December 8, 2010, Michel Lespinasse wrote: >> >> Yes, patch 1/6 changes the long hold time to be in read mode instead >> of write mode, which is only a band-aid. But, this prepares for patch >> 5/6, which releases mmap_sem whenever there is contention on it or >> when blocking on disk reads. > > I have to say that I'm not a huge fan of that horribly kludgy > contention check case. > > The "move page-in to read-locked sequence" and the changes to > get_user_pages look fine, but the contention thing is just disgusting. > I'd really like to see some other approach if at all possible. Andrew, should I amend my patches to remove the rwsem_is_contended() code ? This would involve: - remove rwsem-implement-rwsem_is_contended.patch and x86-rwsem-more-precise-rwsem_is_contended-implementation.patch - in mlock-do-not-hold-mmap_sem-for-extended-periods-of-time.patch, drop the one hunk making use of rwsem_is_contended (rest of the patch would still work without it) - optionally, follow up patch to limit batch size to a constant in do_mlock_pages(): diff --git a/mm/mlock.c b/mm/mlock.c index 569ae6a..a505a7e 100644 --- a/mm/mlock.c +++ b/mm/mlock.c @@ -457,15 +457,23 @@ static int do_mlock_pages(unsigned long start, size_t len) continue; if (nstart < vma->vm_start) nstart = vma->vm_start; + /* + * Constrain batch size to limit mmap_sem hold time. + */ + if (nend > nstart + 1024 * PAGE_SIZE) + nend = nstart + 1024 * PAGE_SIZE; /* * Now fault in a range of pages. __mlock_vma_pages_range() * double checks the vma flags, so that it won't mlock pages * if the vma was already munlocked. */ ret = __mlock_vma_pages_range(vma, nstart, nend, &locked); if (ret < 0) { ret = __mlock_posix_error_return(ret); break; + } else if (locked) { + locked = 0; + up_read(&mm->mmap_sem); } nend = nstart + ret * PAGE_SIZE; ret = 0; I don't really prefer using a constant, but I'm not sure how else to make Linus happy :) -- Michel "Walken" Lespinasse A program is never fully debugged until the last user dies.