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[209.132.183.28]) by mx.google.com with ESMTPS id z20si6162898qvg.220.2019.06.05.03.02.26 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 05 Jun 2019 03:02:27 -0700 (PDT) Received-SPF: pass (google.com: domain of oleg@redhat.com designates 209.132.183.28 as permitted sender) client-ip=209.132.183.28; Authentication-Results: mx.google.com; spf=pass (google.com: domain of oleg@redhat.com designates 209.132.183.28 as permitted sender) smtp.mailfrom=oleg@redhat.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 50645307D90D; Wed, 5 Jun 2019 10:02:12 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.43.17.159]) by smtp.corp.redhat.com (Postfix) with SMTP id 6E49A5C225; Wed, 5 Jun 2019 10:02:09 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Wed, 5 Jun 2019 12:02:11 +0200 (CEST) Date: Wed, 5 Jun 2019 12:02:07 +0200 From: Oleg Nesterov To: Song Liu Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, peterz@infradead.org, rostedt@goodmis.org, mhiramat@kernel.org, kirill.shutemov@linux.intel.com, kernel-team@fb.com, william.kucharski@oracle.com Subject: Re: [PATCH uprobe, thp v2 2/5] uprobe: use original page when all uprobes are removed Message-ID: <20190605100207.GD32406@redhat.com> References: <20190604165138.1520916-1-songliubraving@fb.com> <20190604165138.1520916-3-songliubraving@fb.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190604165138.1520916-3-songliubraving@fb.com> User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.48]); Wed, 05 Jun 2019 10:02:16 +0000 (UTC) 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 06/04, Song Liu wrote: > > Currently, uprobe swaps the target page with a anonymous page in both > install_breakpoint() and remove_breakpoint(). When all uprobes on a page > are removed, the given mm is still using an anonymous page (not the > original page). Agreed, it would be nice to avoid this, > @@ -461,9 +471,10 @@ int uprobe_write_opcode(struct arch_uprobe *auprobe, struct mm_struct *mm, > unsigned long vaddr, uprobe_opcode_t opcode) > { > struct uprobe *uprobe; > - struct page *old_page, *new_page; > + struct page *old_page, *new_page, *orig_page = NULL; > struct vm_area_struct *vma; > int ret, is_register, ref_ctr_updated = 0; > + pgoff_t index; > > is_register = is_swbp_insn(&opcode); > uprobe = container_of(auprobe, struct uprobe, arch); > @@ -501,6 +512,19 @@ int uprobe_write_opcode(struct arch_uprobe *auprobe, struct mm_struct *mm, > copy_highpage(new_page, old_page); > copy_to_page(new_page, vaddr, &opcode, UPROBE_SWBP_INSN_SIZE); > > + index = vaddr_to_offset(vma, vaddr & PAGE_MASK) >> PAGE_SHIFT; > + orig_page = find_get_page(vma->vm_file->f_inode->i_mapping, index); I think you should take is_register into account, if it is true we are going to install the breakpoint so we can avoid find_get_page/pages_identical. > + if (orig_page) { > + if (pages_identical(new_page, orig_page)) { > + /* if new_page matches orig_page, use orig_page */ > + put_page(new_page); > + new_page = orig_page; Hmm. can't we simply unmap the page in this case? Oleg.