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=-7.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS 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 0420AC432BE for ; Fri, 6 Aug 2021 17:42:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DF71B61164 for ; Fri, 6 Aug 2021 17:42:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235916AbhHFRmU (ORCPT ); Fri, 6 Aug 2021 13:42:20 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45702 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231776AbhHFRmS (ORCPT ); Fri, 6 Aug 2021 13:42:18 -0400 Received: from mail-ed1-x52c.google.com (mail-ed1-x52c.google.com [IPv6:2a00:1450:4864:20::52c]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 62D7DC0613CF; Fri, 6 Aug 2021 10:42:02 -0700 (PDT) Received: by mail-ed1-x52c.google.com with SMTP id y12so14108242edo.6; Fri, 06 Aug 2021 10:42:02 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=WM8262vn+lmKFFIbpe3Pl05b0K+86wXg1e1fI17ViY4=; b=AJ/dafNd/fGnNdzTsrGALMC1ppJIDa1ETSbNpAtVQPmCk8gSnKcrSChv/nmltQrGRB 4KZgPX10ZGSPJh0PuALQYIsqzjte6Td/6nGeBZHhBqKHyo3IQ2XoKDCZHOjHsNgJZJ7g VGCEIhhZBmeZ8EuHVZKCDmWy2IpM6kGAwwpQk0q6+JCdKb97G5pjePdw+1PR8LKlOaZT r6Lz/I5kGbrUkRqFKSaH+YP6lkUd3z6x5wDyJHB0/VB92FxvOE6rV5osn5jIgxZ4/s+e YsKptXGbhf4IYGbfMlNq+QQKxVqWil4GFmMjcikc1rZyaNNw9R4bftcGtL/wnxfQGwDP y29Q== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=WM8262vn+lmKFFIbpe3Pl05b0K+86wXg1e1fI17ViY4=; b=oujuUXDgbqylLY2nOj++NCMxvQ2XPSzgfwaa8ydx/aeDkKbfYGg9A4vM7kL9EMhE5Q WM6NRvdzJKnyeP0H24yeW2cmYN8QJmx1XwIZ8RCzIGLY9NdGlp9YwVCUfU9DKuCiBl5J a0frNM33W9i2Pmw35DcQ1XdVRepgEr1SD09wcfJtpCCGNuTjFZtTXTUhkOp7zvDNhAFo ghRec4EORURgVMJVc4Wdf10Md6emN457JRuJ1CYGQJ83DbOoWWNn3i/nRvM1c3V1b8py pOOgrcJmUZoghKW+HBWDvAa8q0aZn052ap5u0H4I20NAbFdWRL2VqXczB0uyjf/nKRxl RxsQ== X-Gm-Message-State: AOAM5313mHbBCbv3em+vvkdo1KcbpBKIXXXW9YD1TrQv7a6u4MlqrEwC dJq5NjjlA35GhEnM/xNdki0fro++bq9/ckZU+fo= X-Google-Smtp-Source: ABdhPJyV7fJS76Tp9PwQ6sfhrCr5CbXvsvm83jzMnP/O6w1bqoLPiQwFuOcPbl8qxv4mdUXP3HpEkCeqxPohGyxg3L4= X-Received: by 2002:a05:6402:386:: with SMTP id o6mr14486287edv.294.1628271721056; Fri, 06 Aug 2021 10:42:01 -0700 (PDT) MIME-Version: 1.0 References: <2862852d-badd-7486-3a8e-c5ea9666d6fb@google.com> <8baad8b2-8f7a-2589-ce21-4135a59c5dc6@google.com> <5add2467-3b23-f8b8-e07b-82d8a573ecb7@google.com> In-Reply-To: <5add2467-3b23-f8b8-e07b-82d8a573ecb7@google.com> From: Yang Shi Date: Fri, 6 Aug 2021 10:41:49 -0700 Message-ID: Subject: Re: [PATCH 06/16] huge tmpfs: shmem_is_huge(vma, inode, index) To: Hugh Dickins Cc: Andrew Morton , Shakeel Butt , "Kirill A. Shutemov" , Miaohe Lin , Mike Kravetz , Michal Hocko , Rik van Riel , Christoph Hellwig , Matthew Wilcox , "Eric W. Biederman" , Alexey Gladkov , Chris Wilson , Matthew Auld , Linux FS-devel Mailing List , Linux Kernel Mailing List , linux-api@vger.kernel.org, Linux MM Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Aug 5, 2021 at 10:21 PM Hugh Dickins wrote: > > On Wed, 4 Aug 2021, Yang Shi wrote: > > On Wed, Aug 4, 2021 at 1:28 AM Hugh Dickins wrote: > > > > > > Thanks, but despite us agreeing that the race is too unlikely to be worth > > > optimizing against, it does still nag at me ever since you questioned it: > > > silly, but I can't quite be convinced by my own dismissals. > > > > > > I do still want to get rid of SGP_HUGE and SGP_NOHUGE, clearing up those > > > huge allocation decisions remains the intention; but now think to add > > > SGP_NOALLOC for collapse_file() in place of SGP_NOHUGE or SGP_CACHE - > > > to rule out that possibility of mischarge after racing hole-punch, > > > no matter whether it's huge or small. If any such race occurs, > > > collapse_file() should just give up. > > > > > > This being the "Stupid me" SGP_READ idea, except that of course would > > > not work: because half the point of that block in collapse_file() is > > > to initialize the !Uptodate pages, whereas SGP_READ avoids doing so. > > > > > > There is, of course, the danger that in fixing this unlikely mischarge, > > > I've got the code wrong and am introducing a bug: here's what a 17/16 > > > would look like, though it will be better inserted early. I got sick > > > of all the "if (page "s, and was glad of the opportunity to fix that > > > outdated "bring it back from swap" comment - swap got done above. > > > > > > What do you think? Should I add this in or leave it out? > > > > Thanks for keeping investigating this. The patch looks good to me. I > > think we could go this way. Just a nit below. > > Thanks, I'll add it into the series, a patch before SGP_NOHUGE goes away; > but I'm not intending to respin the series until there's more feedback > from others - fcntl versus fadvise is the main issue so far. Thanks, yeah, no hurry to repost. > > > > --- a/include/linux/shmem_fs.h > > > +++ b/include/linux/shmem_fs.h > > > @@ -108,6 +108,7 @@ extern unsigned long shmem_partial_swap_usage(struct address_space *mapping, > > > /* Flag allocation requirements to shmem_getpage */ > > > enum sgp_type { > > > SGP_READ, /* don't exceed i_size, don't allocate page */ > > > + SGP_NOALLOC, /* like SGP_READ, but do use fallocated page */ > > > > The comment looks misleading, it seems SGP_NOALLOC does clear the > > Uptodate flag but SGP_READ doesn't. Or it is fine not to distinguish > > this difference? > > I think you meant to say, SGP_NOALLOC does *set* the Uptodate flag but > SGP_READ doesn't. And a more significant difference, as coded to suit > collapse_file(), is that SGP_NOALLOC returns failure on hole, whereas > SGP_READ returns success: I should have mentioned that. Yes, I mean "set". Sorry for the confusion. > > When I wrote "like SGP_READ" there, I just meant "like what's said in > the line above": would "ditto" be okay with you, and I say > SGP_NOALLOC, /* ditto, but fail on hole, or use fallocated page */ > > I don't really want to get into the "Uptodate" business there. > And I'm afraid someone is going to ask me to write multi-line comments > on each of those SGP_flags, and I'm going to plead "read the source"! OK, I'm fine as is. > > Oh, now I see why you said SGP_NOALLOC does clear the Uptodate flag: > "goto clear", haha: when we clear the page we set the Uptodate flag. > > And I may have another patch to slot in: I was half expecting you to > question why SGP_READ behaves as it does, so in preparing its defence > I checked, and found it was not doing quite what I remembered: changes > were made a long time ago, which have left it slightly suboptimal. > But that really has nothing to do with the rest of this series, > and I don't need to run it past you before reposting. > > I hope that some of the features in this series can be useful to you. Thanks, I will see. > > Thanks, > Hugh