From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f48.google.com (mail-wm0-f48.google.com [74.125.82.48]) by kanga.kvack.org (Postfix) with ESMTP id D92236B0009 for ; Fri, 26 Feb 2016 05:37:45 -0500 (EST) Received: by mail-wm0-f48.google.com with SMTP id c200so66401387wme.0 for ; Fri, 26 Feb 2016 02:37:45 -0800 (PST) Received: from mail-wm0-x232.google.com (mail-wm0-x232.google.com. [2a00:1450:400c:c09::232]) by mx.google.com with ESMTPS id cd8si15182846wjc.91.2016.02.26.02.37.44 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 26 Feb 2016 02:37:44 -0800 (PST) Received: by mail-wm0-x232.google.com with SMTP id g62so64448354wme.0 for ; Fri, 26 Feb 2016 02:37:44 -0800 (PST) Date: Fri, 26 Feb 2016 13:37:42 +0300 From: "Kirill A. Shutemov" Subject: Re: THP race? Message-ID: <20160226103742.GC22450@node.shutemov.name> References: <20160223154950.GA22449@node.shutemov.name> <20160223180609.GC23289@redhat.com> <20160223183832.GB21820@node.shutemov.name> <20160223192835.GJ9157@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: Dan Williams Cc: Andrea Arcangeli , linux-mm On Thu, Feb 25, 2016 at 10:45:05AM -0800, Dan Williams wrote: > On Tue, Feb 23, 2016 at 11:28 AM, Andrea Arcangeli wrote: > > On Tue, Feb 23, 2016 at 09:38:32PM +0300, Kirill A. Shutemov wrote: > >> pmd_trans_unstable(pmd), otherwise looks good: > > > > Yes sorry. > > > >> Acked-by: Kirill A. Shutemov > > > > Thanks for the quick ack, I just noticed or I would have added it to > > the resubmit, but it can be still added to -mm. > > > >> BTW, I guess DAX would need to introduce the same infrastructure for > >> pmd_devmap(). Dan? > > > > There is a i_mmap_lock_write in the truncate path that saves the day > > for the pmd zapping in the truncate() case without mmap_sem (the only > > case anon THP doesn't need to care about as truncate isn't possible in > > the anon case), but not in the MADV_DONTNEED madvise case that runs > > only with the mmap_sem for reading. > > > > The only objective of this "infrastructure" is to add no pmd_lock()ing > > overhead to the page fault, if the mapping is already established but > > not huge, and we've just to walk through the pmd to reach the > > pte. All because MADV_DONTNEED is running with the mmap_sem for > > reading unlike munmap and other slower syscalls that are forced to > > mangle the vmas and have to take the mmap_sem for writing regardless. > > > > The question for DAX is if it should do a pmd_devmap check inside > > pmd_none_or_trans_huge_or_clear_bad() after pmd_trans_huge() and get > > away with a one liner, or add its own infrastructure with > > pmd_devmap_unstable(). In the pmd_devmap case the problem isn't just > > in __handle_mm_fault. If it could share the same infrastructure it'd > > be ideal. > > > > Yes, I see no reason why we can't/shoudn't move the pmd_devmap() check > inside pmd_none_or_trans_huge_or_clear_bad(). Are you going take care about this? -- Kirill A. Shutemov -- 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