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 4B9F3C3A5A7 for ; Tue, 3 Sep 2019 12:22:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 212842087E for ; Tue, 3 Sep 2019 12:22:11 +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" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729036AbfICMWK (ORCPT ); Tue, 3 Sep 2019 08:22:10 -0400 Received: from bombadil.infradead.org ([198.137.202.133]:40434 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726631AbfICMWK (ORCPT ); Tue, 3 Sep 2019 08:22:10 -0400 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) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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!