From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.0 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 877F1C432C3 for ; Fri, 29 Nov 2019 11:18:07 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 487DE21774 for ; Fri, 29 Nov 2019 11:18:07 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="jBmdxMS5" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 487DE21774 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id B88406B0579; Fri, 29 Nov 2019 06:18:06 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id B3ADD6B057A; Fri, 29 Nov 2019 06:18:06 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id A281E6B057B; Fri, 29 Nov 2019 06:18:06 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0166.hostedemail.com [216.40.44.166]) by kanga.kvack.org (Postfix) with ESMTP id 8D15D6B0579 for ; Fri, 29 Nov 2019 06:18:06 -0500 (EST) Received: from smtpin23.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with SMTP id 376D36D9D for ; Fri, 29 Nov 2019 11:18:06 +0000 (UTC) X-FDA: 76209065772.23.sleet52_299665c5d9e3e X-HE-Tag: sleet52_299665c5d9e3e X-Filterd-Recvd-Size: 4400 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) by imf42.hostedemail.com (Postfix) with ESMTP for ; Fri, 29 Nov 2019 11:18:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=ZZSK5G9CmqUn+L9Snie2RndpxADqX46kgik9LLqsPOc=; b=jBmdxMS5hFi6GJwiX5wdoNSro qPx2pEgXbYVsCXQNiH4WiWd4MYkNVd8trSnyJmXyGD296jm0i9OvZF9NAUYL6SsTI85feR8owSKJr i8u91HLlyYkRYr2DHxmx/ARNpu7RV8L3jyDtSrWa9VR8oPl4akU3mowdZfcJsLnDgCRN9YTVofpGT fxsU4LJHOjBj1u5jxQrvRvBuOn8yw/oXrTOms3rPr83bV+nv7pJBaeIGRUFoQAFBCVjVjgVv+vkqH tdidYQx9htrcXTa9/zx5Ou4gXmro4VdCaIQQSWEoLk86x1G44+zQieIx9JdQus5WUOHtz5Gbuvuxr /CuPRpEyQ==; Received: from willy by bombadil.infradead.org with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1iaeHh-0006rY-83; Fri, 29 Nov 2019 11:18:01 +0000 Date: Fri, 29 Nov 2019 03:18:01 -0800 From: Matthew Wilcox To: Wei Yang Cc: Wei Yang , "Kirill A. Shutemov" , akpm@linux-foundation.org, kirill.shutemov@linux.intel.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 2/2] mm/page_vma_mapped: page table boundary is already guaranteed Message-ID: <20191129111801.GH20752@bombadil.infradead.org> References: <20191128010321.21730-1-richardw.yang@linux.intel.com> <20191128010321.21730-2-richardw.yang@linux.intel.com> <20191128083143.kwih655snxqa2qnm@box.shutemov.name> <20191128210945.6gtt7wlygsvxip4n@master> <20191128223904.GG20752@bombadil.infradead.org> <20191129083002.GA1669@richard> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191129083002.GA1669@richard> User-Agent: Mutt/1.12.1 (2019-06-15) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Fri, Nov 29, 2019 at 04:30:02PM +0800, Wei Yang wrote: > On Thu, Nov 28, 2019 at 02:39:04PM -0800, Matthew Wilcox wrote: > >On Thu, Nov 28, 2019 at 09:09:45PM +0000, Wei Yang wrote: > >> On Thu, Nov 28, 2019 at 11:31:43AM +0300, Kirill A. Shutemov wrote: > >> >On Thu, Nov 28, 2019 at 09:03:21AM +0800, Wei Yang wrote: > >> >> The check here is to guarantee pvmw->address iteration is limited in one > >> >> page table boundary. To be specific, here the address range should be in > >> >> one PMD_SIZE. > >> >> > >> >> If my understanding is correct, this check is already done in the above > >> >> check: > >> >> > >> >> address >= __vma_address(page, vma) + PMD_SIZE > >> >> > >> >> The boundary check here seems not necessary. > >> >> > >> >> Signed-off-by: Wei Yang > >> > > >> >NAK. > >> > > >> >THP can be mapped with PTE not aligned to PMD_SIZE. Consider mremap(). > >> > > >> > >> Hi, Kirill > >> > >> Thanks for your comment during Thanks Giving Day. Happy holiday:-) > >> > >> I didn't think about this case before, thanks for reminding. Then I tried to > >> understand your concern. > >> > >> mremap() would expand/shrink a memory mapping. In this case, probably shrink > >> is in concern. Since pvmw->page and pvmw->vma are not changed in the loop, the > >> case you mentioned maybe pvmw->page is the head of a THP but part of it is > >> unmapped. > > > >mremap() can also move a mapping, see MREMAP_FIXED. > > Hi, Matthew > > Thanks for your comment. > > I took a look into the MREMAP_FIXED case, but still not clear in which case it > fall into the situation Kirill mentioned. > > Per my understanding, move mapping is achieved in two steps: > > * unmap some range in old vma if old_len >= new_len > * move vma > > If the length doesn't change, we are expecting to have the "copy" of old > vma. This doesn't change the THP PMD mapping. > > So the change still happens in the unmap step, if I am correct. > > Would you mind giving me more hint on the case when we would have the > situation as Kirill mentioned? Set up a THP mapping. Move it to an address which is no longer 2MB aligned. Unmap it.