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=-2.1 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=no 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 DC64BC3A5A2 for ; Tue, 3 Sep 2019 12:22:15 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 9BECB2087E for ; Tue, 3 Sep 2019 12:22:15 +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="sdAJgqyO" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 9BECB2087E 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 28BA96B0003; Tue, 3 Sep 2019 08:22:15 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 23B896B0005; Tue, 3 Sep 2019 08:22:15 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 104546B0006; Tue, 3 Sep 2019 08:22:15 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0113.hostedemail.com [216.40.44.113]) by kanga.kvack.org (Postfix) with ESMTP id E50D46B0003 for ; Tue, 3 Sep 2019 08:22:14 -0400 (EDT) Received: from smtpin20.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with SMTP id 85EEC180AD7C3 for ; Tue, 3 Sep 2019 12:22:14 +0000 (UTC) X-FDA: 75893521788.20.copy35_30a05d9198323 X-HE-Tag: copy35_30a05d9198323 X-Filterd-Recvd-Size: 3750 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) by imf25.hostedemail.com (Postfix) with ESMTP for ; Tue, 3 Sep 2019 12:22:14 +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=ccUGFVNxssVWDcbI4ftnmg58MbgKoeWD8Ifd/JsATGA=; b=sdAJgqyOjMVv5fGaTpFicA5RP 0MALv5u8khHy2K9Yl7P37X5h9KAHJlerdtdvJhnb3lJKI4pzP9dQt487I46HmBIrgC7njktl3YgWa SQWOLRQhasxNetbiJq1YJk4ow8C0kTd+vCWMFmUZ6CEBLYUz/expOYSTwdf+ImbTf9OT3sMVRk3t6 djywTV4fdBXWnWMXlOtU+Cat+AE2NfVI1wgF9MBF2jwWESybVK2yGLv3CBrmVVHgms+SvUPg8M7I3 iEbvurEHnm0jQ2rV1vxDYUqKxI+1SX8YNQGuHQUesSirCQB4QGmdBwrzX3+BvYyxkIGXP6l3GDVH7 QA3EPd7bg==; Received: from willy by bombadil.infradead.org with local (Exim 4.92 #3 (Red Hat Linux)) id 1i57p2-0006Fn-RW; Tue, 03 Sep 2019 12:22:08 +0000 Date: Tue, 3 Sep 2019 05:22:08 -0700 From: Matthew Wilcox To: Michal Hocko Cc: William Kucharski , linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, Dave Hansen , Song Liu , Bob Kasten , Mike Kravetz , Chad Mynhier , "Kirill A. Shutemov" , Johannes Weiner Subject: Re: [PATCH v5 2/2] mm,thp: Add experimental config option RO_EXEC_FILEMAP_HUGE_FAULT_THP Message-ID: <20190903122208.GE29434@bombadil.infradead.org> References: <20190902092341.26712-1-william.kucharski@oracle.com> <20190902092341.26712-3-william.kucharski@oracle.com> <20190903121424.GT14028@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190903121424.GT14028@dhcp22.suse.cz> User-Agent: Mutt/1.11.4 (2019-03-13) 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 Tue, Sep 03, 2019 at 02:14:24PM +0200, Michal Hocko wrote: > On Mon 02-09-19 03:23:41, William Kucharski wrote: > > Add filemap_huge_fault() to attempt to satisfy page > > faults on memory-mapped read-only text pages using THP when possible. > > This deserves much more description of how the thing is implemented and > expected to work. For one thing it is not really clear to me why you > need CONFIG_RO_EXEC_FILEMAP_HUGE_FAULT_THP at all. You need a support > from the filesystem anyway. So who is going to enable/disable this > config? There are definitely situations in which enabling this code will crash the kernel. But we want to get filesystems to a point where they can start working on their support for large pages. So our workaround is to try to get the core pieces merged under a CONFIG_I_KNOW_WHAT_IM_DOING flag and let people play with it. Then continue to work on the core to eliminate those places that are broken. > I cannot really comment on fs specific parts but filemap_huge_fault > sounds convoluted so much I cannot wrap my head around it. One thing > stand out though. The generic filemap_huge_fault depends on ->readpage > doing the right thing which sounds quite questionable to me. If nothing > else I would expect ->readpages to do the job. Ah, that's because you're not a filesystem person ;-) ->readpages is really ->readahead. It's a crappy interface and should be completely redesigned. Thanks for looking!