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=-7.5 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A, 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 73F69C4320A for ; Thu, 2 Sep 2021 07:05:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5BD31600EF for ; Thu, 2 Sep 2021 07:05:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S242688AbhIBHGE (ORCPT ); Thu, 2 Sep 2021 03:06:04 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59306 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S240424AbhIBHGB (ORCPT ); Thu, 2 Sep 2021 03:06:01 -0400 Received: from mail-pj1-x1035.google.com (mail-pj1-x1035.google.com [IPv6:2607:f8b0:4864:20::1035]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 5B56AC061757 for ; Thu, 2 Sep 2021 00:05:03 -0700 (PDT) Received: by mail-pj1-x1035.google.com with SMTP id z24-20020a17090acb1800b0018e87a24300so806606pjt.0 for ; Thu, 02 Sep 2021 00:05:03 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=bytedance-com.20150623.gappssmtp.com; s=20150623; h=subject:to:cc:references:from:message-id:date:user-agent :mime-version:in-reply-to:content-transfer-encoding; bh=HBaL61QBYMUZzotrZtJQEFy+kr+3Pv8VSTjmOd/YXyc=; b=gpq0+vByj5ZSakSAjmhB412QEKXYdbHQRt6Wrovgsdv2THWPRdvv7VmHPJny18IvW+ UL1jW2O4X/utRsV9mUkdSIDkSjQSAanBZ1D2yv9r8aWO1lk5a4v1/IUhviaTUCXodQEH M0VoNSQ/S9BxwE7HaYDjf/fxqmYskFlTkyRwXEaLM4hrpTgIXVpavUM7mVUEvdoFgDt9 XN1AO6niSrcOKJo2Xcp8ituadZv38hO1gg7ZUbIMVvGQC2alXEORX5t2puTz2wmEkFIQ UxmW3iWRbxPxbHbSome9N7OF+K4bSIQ8zqa144SZUhifjaFwwIg8+f4GeA2BmK7clJ84 2bDA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:cc:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-transfer-encoding; bh=HBaL61QBYMUZzotrZtJQEFy+kr+3Pv8VSTjmOd/YXyc=; b=Mcslsl0QnJDRW17yFUESbik9k6aUcIHP+IopbRQfslyk6YYkkgICRx3rO0iltKYeuh LrW3844tMW60PUIlcqNgNGpSJENnUDqT3sDuqeg7mNqK9eDvSV/XYTZlteqk7Hi4Jit6 Vyj12celhCIncEZprtzPJZ1V/bUk5IZam22AdL/5qFAtfXl/9Cwukj7AFBU7sakiOxth yzTCqvFY1uOeof2oSLhPG8yFmMHlsh+C7U0UaH/Gd1kgvjjLDmQ9q1Ry4JhdwEFl5xZn 26rPtpIgOU74m74BqqrL4dwq/GkEEwni22AbiOTMEKpWjXp0j1eXWtMeefAOoCn14CIj PdGQ== X-Gm-Message-State: AOAM5320KT97mkznrC88PjAj8eZWvLalm7xyPdodZSz+j7bu16ZfGkIH YyBUFdKjcBbkDtWexPyVohGRPg== X-Google-Smtp-Source: ABdhPJwpJqPKt9Y7iE8kwSXxa86EER+DXHn4/hF1fRP/w8Fj/bNnbhwN4Ru5ZqkqVVCTzkNLo39/kw== X-Received: by 2002:a17:90a:d990:: with SMTP id d16mr2305089pjv.2.1630566302822; Thu, 02 Sep 2021 00:05:02 -0700 (PDT) Received: from [10.254.207.253] ([139.177.225.243]) by smtp.gmail.com with ESMTPSA id ev12sm984854pjb.57.2021.09.02.00.04.56 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 02 Sep 2021 00:05:02 -0700 (PDT) Subject: Re: [PATCH v2 6/9] mm: free user PTE page table pages To: Jason Gunthorpe , David Hildenbrand Cc: akpm@linux-foundation.org, tglx@linutronix.de, hannes@cmpxchg.org, mhocko@kernel.org, vdavydov.dev@gmail.com, kirill.shutemov@linux.intel.com, mika.penttila@nextfour.com, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, songmuchun@bytedance.com References: <20210819031858.98043-1-zhengqi.arch@bytedance.com> <20210819031858.98043-7-zhengqi.arch@bytedance.com> <20210901135314.GA1859446@nvidia.com> <0c9766c9-6e8b-5445-83dc-9f2b71a76b4f@redhat.com> <20210901153247.GJ1721383@nvidia.com> <7789261d-6a64-c47b-be6c-c9be680e5d33@redhat.com> <20210901161613.GN1721383@nvidia.com> <20210901171039.GO1721383@nvidia.com> <20210901175547.GP1721383@nvidia.com> From: Qi Zheng Message-ID: Date: Thu, 2 Sep 2021 15:04:53 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.13.0 MIME-Version: 1.0 In-Reply-To: <20210901175547.GP1721383@nvidia.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2021/9/2 AM1:55, Jason Gunthorpe wrote: > On Wed, Sep 01, 2021 at 07:49:23PM +0200, David Hildenbrand wrote: >> On 01.09.21 19:10, Jason Gunthorpe wrote: >>> On Wed, Sep 01, 2021 at 06:19:03PM +0200, David Hildenbrand wrote: >>> >>>>> I wouldn't think it works everywhere, bit it works in a lot of places, >>>>> and it is a heck of a lot better than what is proposed here. I'd >>>>> rather see the places that can use it be moved, and the few places >>>>> that can't be opencoded. >>>> >>>> Well, I used ptep_get_map_lock() and friends. But hacking directly into >>>> ptep_map_lock() and friends wasn't possible due to all the corner cases. >>> >>> Sure, I'm not surprised you can't get every single case, but that just >>> suggest we need two API families, today's to support the special cases >>> and a different one for the other regular simple cases. >>> >>> A new function family pte_try_map/_locked() and paired unmap that can >>> internally do the recounting and THP trickery and convert the easy >>> callsites. >>> >>> Very rough counting suggest at least half of the pte_offset_map_lock() >>> call sites can trivially use the simpler API. >>> >>> The other cases can stay as is and get open coded refcounts, or maybe >>> someone will have a better idea once they are more clearly identified. >>> >>> But I don't think we should take a performance hit of additional >>> atomics in cases like GUP where this is trivially delt with by using a >>> better API. >> >> Right, but as I said in the cover letter, we can happily optimize once we >> have the basic infrastructure in place and properly reviewed. Getting rid of >> some unnecessary atomics by introducing additional fancy helpers falls under >> that category. > > I'm not sure I agree given how big and wide this patch series is. It > would be easier to review if it was touching less places. The helpers > are not fancy, it is a logical re-arrangement of existing code that > shrinks the LOC of this series and makes it more reviewable. > > Or stated another way, a niche feature like this try much harder not > to add more complexity everywhere. Totally agree, I will rework this patch series based on you and David's suggestions. Thank you very much, Qi > > Jason >