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=-2.2 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT 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 41825C04AB3 for ; Thu, 9 May 2019 16:49:19 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id EAB222177E for ; Thu, 9 May 2019 16:49:18 +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="ngKRs85U" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org EAB222177E 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 8C33F6B0007; Thu, 9 May 2019 12:49:18 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 825946B0008; Thu, 9 May 2019 12:49:18 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 69EB56B000A; Thu, 9 May 2019 12:49:18 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from mail-pl1-f199.google.com (mail-pl1-f199.google.com [209.85.214.199]) by kanga.kvack.org (Postfix) with ESMTP id 31D196B0007 for ; Thu, 9 May 2019 12:49:18 -0400 (EDT) Received: by mail-pl1-f199.google.com with SMTP id 61so805110plr.21 for ; Thu, 09 May 2019 09:49:18 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:dkim-signature:date:from:to:cc:subject :message-id:references:mime-version:content-disposition:in-reply-to :user-agent; bh=gE30E8WxB7hYkwUgNS86rgGRZVvaab/3r9G8N035r+M=; b=ddysf4ubtKId+UfH6xBU7JRw9gMGk9/Rsm3tvCs1J/zFB4dSNCdaHpi3oUAczIj+Z7 6hvF9FhVGvAb6nbtQ/qMacqZUWdQcPjf0zzBWsZLAdo0UszTfynQOrZfWVNszLvCYoAc 6txS3q7ACrmWdXKojthnoxSjQZjB+K8m78RW6fU41d3Y86jbPfSAyia8znTvF44qOlqs /CDHn9LgUlcN55MWcb/zuwwbP1kJDjh0xC/qtROjuEjRn/xswIhCdrxGvcucO6A3bO/C zJg4Sn1Zxg3nOOR+94Qa8G17lV3ZqTkwdgmRqZFF592ZZocYyu8kQgDiDrDmtHTwGrJu W8Sw== X-Gm-Message-State: APjAAAXOjajPxaLo3asag2/tXaDoT8efvVn681iDV/6rrCLa84nWOXKt MFjC/Bd3LaCorZu1ipqB92B0dOLB+b/g8W6ONJxvjuiPru9v3IUQ+0hP70xqnpAZSDf9M6ubhOj WAmNiBh9WccSwsjZLqYejWrnxRW3b1Lc/vT9RAseNXoBHAetf3YBx6JqOOdbcF6hLhw== X-Received: by 2002:aa7:9ac4:: with SMTP id x4mr6705494pfp.43.1557420557717; Thu, 09 May 2019 09:49:17 -0700 (PDT) X-Google-Smtp-Source: APXvYqwJnENtUYQ4r4ZLhFzaSJtQvgCw2zm9JTPk1UaKq1ygUO/xdHBjzu0zxkueREY1g5j2IOwF X-Received: by 2002:aa7:9ac4:: with SMTP id x4mr6705401pfp.43.1557420556975; Thu, 09 May 2019 09:49:16 -0700 (PDT) ARC-Seal: i=1; a=rsa-sha256; t=1557420556; cv=none; d=google.com; s=arc-20160816; b=KxwNSKKFeIjWh/1SvKGzNbXVWE2/t8KBM6nBmH53QOyQWDBgNo6c9u7aRAi4Evgwci yLgZcxoH7yo+io1wZflEF5LSDsXD++gnJ2LFjDO3IFGsWKOCwaSNHzmrIEGKkloPD51u NefR9XTHT02KYDuVdfJhv8BBdHeOOLplmVqBkMYzSVA5H/vGDMuhiFW9Rqu1xq8KzLys RoV1x43fi+FaFQ4lItFqgzLU0WU0MiWzSccPBk4UkPsfsx8MUwDOYdYgoS2gzBXUQM8V CY2PwZ+kiwmWV2Tw+pbEPIF2MxQOxYZprQYBRAOb7TQm4TXT3ul0KdcxPKqOsvKrBsUq FTMg== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=user-agent:in-reply-to:content-disposition:mime-version:references :message-id:subject:cc:to:from:date:dkim-signature; bh=gE30E8WxB7hYkwUgNS86rgGRZVvaab/3r9G8N035r+M=; b=IEPLJ5QL/w7kNExe+0PqPxQLer9j5vpFwWlEHT0gdESftduIOce7asn0lvXImhTNNd x6eYgm5G1z+3NJygPNiYRYrKO6ppuR+8kQJrQat1TQD9bVmK5wzaguyX+KFGwCGvpZnA igZ9queNTn0xnhDeUSZLf4Ow0Kx3EYoapapIAvTq9aaZ5RNn5Zx0p9e9VBBgY9Q9zaVt rUReXPjiCfwEvohZYzlXlU+qUJ/5hQGi5+Vt7grfYhKyYg+QU4eCpNP1DnTnzkgibZ7o xzxL0iswxeruBmyi+KCt7u0ykHHzxjEj+aXwsRs0ywrKqVFABVXCQzjGXq90SSpW5l2c Z0mQ== ARC-Authentication-Results: i=1; mx.google.com; dkim=pass header.i=@infradead.org header.s=bombadil.20170209 header.b=ngKRs85U; spf=pass (google.com: best guess record for domain of willy@infradead.org designates 2607:7c80:54:e::133 as permitted sender) smtp.mailfrom=willy@infradead.org Received: from bombadil.infradead.org (bombadil.infradead.org. [2607:7c80:54:e::133]) by mx.google.com with ESMTPS id f7si3820372pgq.522.2019.05.09.09.49.16 for (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Thu, 09 May 2019 09:49:16 -0700 (PDT) Received-SPF: pass (google.com: best guess record for domain of willy@infradead.org designates 2607:7c80:54:e::133 as permitted sender) client-ip=2607:7c80:54:e::133; Authentication-Results: mx.google.com; dkim=pass header.i=@infradead.org header.s=bombadil.20170209 header.b=ngKRs85U; spf=pass (google.com: best guess record for domain of willy@infradead.org designates 2607:7c80:54:e::133 as permitted sender) smtp.mailfrom=willy@infradead.org 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=gE30E8WxB7hYkwUgNS86rgGRZVvaab/3r9G8N035r+M=; b=ngKRs85UnQEDP1Ga/hab969hD GJhNmb9d7tPvBnkqLCuslGiXSWmVI/YSrhJAMIgJuJwkw746cyxl7cwv8I6dGzS6Junajeay76jrx HR2KCrYlqSTd3LCJXwhsGsmRX2EzQ5w4lmVfrYKm9xKmhkuTwxeDVt10+iLMa0liuT/qBloRrFU9+ +s9EaOjVbm3Po1En6NrE1SP2yh58GpTqxbb0d2n15TtyBbMpGFzuaUU9mOnubwtx3OetcFPcCQx0z N8Xo9IhQywCFx1ybna0TEVHom1/suyCkds4AdGVeWmPkgZ5kmq0oABWghyswJnZyRZly6+T9heD12 /O8LeqsOw==; Received: from willy by bombadil.infradead.org with local (Exim 4.90_1 #2 (Red Hat Linux)) id 1hOmEM-0004xN-Cr; Thu, 09 May 2019 16:49:14 +0000 Date: Thu, 9 May 2019 09:49:14 -0700 From: Matthew Wilcox To: Larry Bassel Cc: mike.kravetz@oracle.com, dan.j.williams@intel.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-nvdimm@lists.01.org Subject: Re: [PATCH, RFC 2/2] Implement sharing/unsharing of PMDs for FS/DAX Message-ID: <20190509164914.GA3862@bombadil.infradead.org> References: <1557417933-15701-1-git-send-email-larry.bassel@oracle.com> <1557417933-15701-3-git-send-email-larry.bassel@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1557417933-15701-3-git-send-email-larry.bassel@oracle.com> User-Agent: Mutt/1.9.2 (2017-12-15) 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 Thu, May 09, 2019 at 09:05:33AM -0700, Larry Bassel wrote: > This is based on (but somewhat different from) what hugetlbfs > does to share/unshare page tables. Wow, that worked out far more cleanly than I was expecting to see. > @@ -4763,6 +4763,19 @@ void adjust_range_if_pmd_sharing_possible(struct vm_area_struct *vma, > unsigned long *start, unsigned long *end) > { > } > + > +unsigned long page_table_shareable(struct vm_area_struct *svma, > + struct vm_area_struct *vma, > + unsigned long addr, pgoff_t idx) > +{ > + return 0; > +} > + > +bool vma_shareable(struct vm_area_struct *vma, unsigned long addr) > +{ > + return false; > +} I don't think you need these stubs, since the only caller of them is also gated by MAY_SHARE_FSDAX_PMD ... right? > + vma_interval_tree_foreach(svma, &mapping->i_mmap, idx, idx) { > + if (svma == vma) > + continue; > + > + saddr = page_table_shareable(svma, vma, addr, idx); > + if (saddr) { > + spmd = huge_pmd_offset(svma->vm_mm, saddr, > + vma_mmu_pagesize(svma)); > + if (spmd) { > + get_page(virt_to_page(spmd)); > + break; > + } > + } > + } I'd be tempted to reduce the indentation here: vma_interval_tree_foreach(svma, &mapping->i_mmap, idx, idx) { if (svma == vma) continue; saddr = page_table_shareable(svma, vma, addr, idx); if (!saddr) continue; spmd = huge_pmd_offset(svma->vm_mm, saddr, vma_mmu_pagesize(svma)); if (spmd) break; } > + if (!spmd) > + goto out; ... and move the get_page() down to here, so we don't split the "when we find it" logic between inside and outside the loop. get_page(virt_to_page(spmd)); > + > + ptl = pmd_lockptr(mm, spmd); > + spin_lock(ptl); > + > + if (pud_none(*pud)) { > + pud_populate(mm, pud, > + (pmd_t *)((unsigned long)spmd & PAGE_MASK)); > + mm_inc_nr_pmds(mm); > + } else { > + put_page(virt_to_page(spmd)); > + } > + spin_unlock(ptl); > +out: > + pmd = pmd_alloc(mm, pud, addr); > + i_mmap_unlock_write(mapping); I would swap these two lines. There's no need to hold the i_mmap_lock while allocating this PMD, is there? I mean, we don't for the !may_share case.