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 Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id BBF3CCCA482 for ; Tue, 7 Jun 2022 21:27:23 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 03AB38D0003; Tue, 7 Jun 2022 17:27:23 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id F2CF26B007B; Tue, 7 Jun 2022 17:27:22 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id DCCA58D0003; Tue, 7 Jun 2022 17:27:22 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) by kanga.kvack.org (Postfix) with ESMTP id CE1DC6B0072 for ; Tue, 7 Jun 2022 17:27:22 -0400 (EDT) Received: from smtpin19.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay12.hostedemail.com (Postfix) with ESMTP id A78CE120C9B for ; Tue, 7 Jun 2022 21:27:22 +0000 (UTC) X-FDA: 79552725924.19.5647148 Received: from mail-pf1-f173.google.com (mail-pf1-f173.google.com [209.85.210.173]) by imf05.hostedemail.com (Postfix) with ESMTP id BD9B2100006 for ; Tue, 7 Jun 2022 21:27:20 +0000 (UTC) Received: by mail-pf1-f173.google.com with SMTP id p8so16607467pfh.8 for ; Tue, 07 Jun 2022 14:27:22 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=RUC7DO64yOo8iCLz5pRqyn0XZn9opq9hvCQSmRWwmeA=; b=WeZICtojSq9fSkf6+sCBJgiX18pXyvfKYbgWg+LAxhl0ZIpQGLN8AufxApccBT5yjA iZ3Em/L4AF2ITnspJQ9DdbyK/NhnqP8SNuimOHW/dfAxLeL/3VTUFmtoNNGzobSdSTqf 6xp0fVsGtUiuD2bu2990Gx9cuxAjd/6W6lAX2GHaHbbY898u7HXF0a7q4pz2VeCfKRVT EUvCDgLEFPE667OoCwOHbOkTdAjhQ469ZEGPcrsNY2MWGyQD6CLF56VRMWW/q6HQNmWM X5H++nujZWGPXc7W2bZCC91lxI7dkR/D9OXz+1NcgEK3peeEs6aHO6QWza6/eV7A784c flrA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=RUC7DO64yOo8iCLz5pRqyn0XZn9opq9hvCQSmRWwmeA=; b=ma2o3R9XMdL/KrgHF0MnpsBY1Q3+UVmJzQqO7DWh7lVnseMyfqg8eg6imvPiPGBCIc Jj+dkptw8sdASkksLdZhNftGzPhA0vsKD2evAZdVyGJxlOm6xMAwm8tbrmi7IoDUt2vx 4WQ9q5mwdENLOb2yKHRm+SR0Ncx8M3xETJnkZMMC7JTLm1HbFTvHhtDElINkEtEYKBaO VT70dY0hxChxs3CAZlDGmm1KN0agrrtiqe0h/x0guqvxOLNdp1pUBLi1Tt2WaJpQpiHe 27V5jHx58Xesf88LDzVtV8UFHfyrEduf+UadhcNca/dfq1c8ltEcCSAsHG82eehsEPF6 mAPg== X-Gm-Message-State: AOAM531sCFrRgC/02C3uSt2xbsUVhXKU0oTNP58Lc+kRc2FJPXMPmuRw vmYjFCqbP3sSJu9In5k9ejxE4OiEk4svBD6Zp2k= X-Google-Smtp-Source: ABdhPJxC7wOntNW7RNZ1X3P3OIyM8tqg2uwGGYY5DnKywFoKB5g02LT/YfnoYRAlxYoVymXl6htVHaHlqwTz9VEp/fM= X-Received: by 2002:a05:6a02:184:b0:3fc:3b43:e5da with SMTP id bj4-20020a056a02018400b003fc3b43e5damr26398040pgb.587.1654637241119; Tue, 07 Jun 2022 14:27:21 -0700 (PDT) MIME-Version: 1.0 References: <20220604004004.954674-1-zokeefe@google.com> <20220604004004.954674-3-zokeefe@google.com> In-Reply-To: From: Yang Shi Date: Tue, 7 Jun 2022 14:27:08 -0700 Message-ID: Subject: Re: [PATCH v6 02/15] mm/khugepaged: record SCAN_PMD_MAPPED when scan_pmd() finds THP To: "Zach O'Keefe" Cc: Alex Shi , David Hildenbrand , David Rientjes , Matthew Wilcox , Michal Hocko , Pasha Tatashin , Peter Xu , Rongwei Wang , SeongJae Park , Song Liu , Vlastimil Babka , Zi Yan , Linux MM , Andrea Arcangeli , Andrew Morton , Arnd Bergmann , Axel Rasmussen , Chris Kennelly , Chris Zankel , Helge Deller , Hugh Dickins , Ivan Kokshaysky , "James E.J. Bottomley" , Jens Axboe , "Kirill A. Shutemov" , Matt Turner , Max Filippov , Miaohe Lin , Minchan Kim , Patrick Xia , Pavel Begunkov , Thomas Bogendoerfer Content-Type: text/plain; charset="UTF-8" X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: BD9B2100006 X-Stat-Signature: fxax3x1hitp4gdxzc1ynhprp4r7t3h78 X-Rspam-User: Authentication-Results: imf05.hostedemail.com; dkim=pass header.d=gmail.com header.s=20210112 header.b=WeZICtoj; spf=pass (imf05.hostedemail.com: domain of shy828301@gmail.com designates 209.85.210.173 as permitted sender) smtp.mailfrom=shy828301@gmail.com; dmarc=pass (policy=none) header.from=gmail.com X-HE-Tag: 1654637240-173727 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, Jun 7, 2022 at 12:33 PM Zach O'Keefe wrote: > > On Tue, Jun 7, 2022 at 9:01 AM Zach O'Keefe wrote: > > > > On Mon, Jun 6, 2022 at 1:46 PM Yang Shi wrote: > > > > > > On Fri, Jun 3, 2022 at 5:40 PM Zach O'Keefe wrote: > > > > > > > > When scanning an anon pmd to see if it's eligible for collapse, return > > > > SCAN_PMD_MAPPED if the pmd already maps a THP. Note that > > > > SCAN_PMD_MAPPED is different from SCAN_PAGE_COMPOUND used in the > > > > file-collapse path, since the latter might identify pte-mapped compound > > > > pages. This is required by MADV_COLLAPSE which necessarily needs to > > > > know what hugepage-aligned/sized regions are already pmd-mapped. > > > > > > > > Signed-off-by: Zach O'Keefe > > > > --- > > > > include/trace/events/huge_memory.h | 1 + > > > > mm/internal.h | 1 + > > > > mm/khugepaged.c | 32 ++++++++++++++++++++++++++---- > > > > mm/rmap.c | 15 ++++++++++++-- > > > > 4 files changed, 43 insertions(+), 6 deletions(-) > > > > > > > > diff --git a/include/trace/events/huge_memory.h b/include/trace/events/huge_memory.h > > > > index d651f3437367..55392bf30a03 100644 > > > > --- a/include/trace/events/huge_memory.h > > > > +++ b/include/trace/events/huge_memory.h > > > > @@ -11,6 +11,7 @@ > > > > EM( SCAN_FAIL, "failed") \ > > > > EM( SCAN_SUCCEED, "succeeded") \ > > > > EM( SCAN_PMD_NULL, "pmd_null") \ > > > > + EM( SCAN_PMD_MAPPED, "page_pmd_mapped") \ > > > > EM( SCAN_EXCEED_NONE_PTE, "exceed_none_pte") \ > > > > EM( SCAN_EXCEED_SWAP_PTE, "exceed_swap_pte") \ > > > > EM( SCAN_EXCEED_SHARED_PTE, "exceed_shared_pte") \ > > > > diff --git a/mm/internal.h b/mm/internal.h > > > > index 6e14749ad1e5..f768c7fae668 100644 > > > > --- a/mm/internal.h > > > > +++ b/mm/internal.h > > > > @@ -188,6 +188,7 @@ extern void reclaim_throttle(pg_data_t *pgdat, enum vmscan_throttle_state reason > > > > /* > > > > * in mm/rmap.c: > > > > */ > > > > +pmd_t *mm_find_pmd_raw(struct mm_struct *mm, unsigned long address); > > > > extern pmd_t *mm_find_pmd(struct mm_struct *mm, unsigned long address); > > > > > > > > /* > > > > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > > > > index cc3d6fb446d5..7a914ca19e96 100644 > > > > --- a/mm/khugepaged.c > > > > +++ b/mm/khugepaged.c > > > > @@ -28,6 +28,7 @@ enum scan_result { > > > > SCAN_FAIL, > > > > SCAN_SUCCEED, > > > > SCAN_PMD_NULL, > > > > + SCAN_PMD_MAPPED, > > > > SCAN_EXCEED_NONE_PTE, > > > > SCAN_EXCEED_SWAP_PTE, > > > > SCAN_EXCEED_SHARED_PTE, > > > > @@ -901,6 +902,31 @@ static int hugepage_vma_revalidate(struct mm_struct *mm, unsigned long address, > > > > return 0; > > > > } > > > > > > > > +static int find_pmd_or_thp_or_none(struct mm_struct *mm, > > > > + unsigned long address, > > > > + pmd_t **pmd) > > > > +{ > > > > + pmd_t pmde; > > > > + > > > > + *pmd = mm_find_pmd_raw(mm, address); > > > > + if (!*pmd) > > > > + return SCAN_PMD_NULL; > > > > + > > > > + pmde = pmd_read_atomic(*pmd); > > > > + > > > > +#ifdef CONFIG_TRANSPARENT_HUGEPAGE > > > > + /* See comments in pmd_none_or_trans_huge_or_clear_bad() */ > > > > + barrier(); > > > > +#endif > > > > + if (!pmd_present(pmde)) > > > > + return SCAN_PMD_NULL; > > > > + if (pmd_trans_huge(pmde)) > > > > + return SCAN_PMD_MAPPED; > > > > + if (pmd_bad(pmde)) > > > > + return SCAN_FAIL; > > > > > > khugepaged doesn't handle pmd_bad before, IIRC it may just return > > > SCAN_SUCCEED if everything else is good? It is fine to add it, but it > > > may be better to return SCAN_PMD_NULL? > > > > Correct, pmd_bad() wasn't handled before. I actually don't know how a > > bad pmd might arise in the wild (would love to actually know this), > > but I don't see the check hurting (might be overly convervative > > though). Conversely, I'm not sure where things go astray currently if > > the pmd is bad. Guess it depends in what way the flags are mutated. > > Returning SCAN_PMD_NULL SGTM. > > > > > > > > > + return SCAN_SUCCEED; > > > > +} > > > > + > > > > /* > > > > * Bring missing pages in from swap, to complete THP collapse. > > > > * Only done if khugepaged_scan_pmd believes it is worthwhile. > > > > @@ -1146,11 +1172,9 @@ static int khugepaged_scan_pmd(struct mm_struct *mm, > > > > > > > > VM_BUG_ON(address & ~HPAGE_PMD_MASK); > > > > > > > > - pmd = mm_find_pmd(mm, address); > > > > - if (!pmd) { > > > > - result = SCAN_PMD_NULL; > > > > + result = find_pmd_or_thp_or_none(mm, address, &pmd); > > > > + if (result != SCAN_SUCCEED) > > > > > > There are a couple of other callsites for mm_find_pmd(), you may need > > > to change all of them to find_pmd_or_thp_or_none() for MADV_COLLAPSE > > > since khugepaged may collapse the area before MADV_COLLAPSE > > > reacquiring mmap_lock IIUC and MADV_COLLAPSE does care this case. It > > > is fine w/o MADV_COLLAPSE since khupaged doesn't care if it is PMD > > > mapped or not. > > > > Ya, I was just questioning the same thing after responding above - at > > least w.r.t whether the pmd_bad() also needs to be in these callsites > > (check for pmd mapping, as you mention, I think is definitely > > necessary). Thanks for catching this! > > > > > So it may be better to move this patch right before MADV_COLLAPSE is introduced? > > > > I think this should be ok - I'll give it a try at least. > > > > Again, thank you for taking the time to thoroughly review this. > > > > Best, > > Zach > > > > > > goto out; > > > > - } > > > > > > > > memset(khugepaged_node_load, 0, sizeof(khugepaged_node_load)); > > > > pte = pte_offset_map_lock(mm, pmd, address, &ptl); > > > > diff --git a/mm/rmap.c b/mm/rmap.c > > > > index 04fac1af870b..c9979c6ad7a1 100644 > > > > --- a/mm/rmap.c > > > > +++ b/mm/rmap.c > > > > @@ -767,13 +767,12 @@ unsigned long page_address_in_vma(struct page *page, struct vm_area_struct *vma) > > > > return vma_address(page, vma); > > > > } > > > > > > > > -pmd_t *mm_find_pmd(struct mm_struct *mm, unsigned long address) > > > > +pmd_t *mm_find_pmd_raw(struct mm_struct *mm, unsigned long address) > > > > > > May be better to have some notes for mm_find_pmd_raw() and mm_find_pmd(). > > > > > Agreed. Looking over this code again, there are only 3 users of mm_find_pmd(): > > 1) khugepaged > 2) ksm (replace_page()) > 3) split_huge_pmd_address() > > Once khugepaged codepaths care about THP-pmds, ksm is the only > remaining user that really wants a pte-mapping pmd. > > I've gone and consolidated the open-coded code in > split_huge_pmd_address() to use the mm_find_pmd_raw(). > > I've also done a name switch: > > mm_find_pmd() -> mm_find_pte_pmd() > mm_find_pmd_raw() -> mm_find_pmd() If ksm is the only user of *current* mm_find_pmd(), I think you should be able to open code it w/o introducing mm_find_pte_pmd() and revert mm_find_pmd() to its *old* behavior. > > This basically reverts mm_find_pmd() to its pre commit f72e7dcdd252 > ("mm: let mm_find_pmd fix buggy race with THP fault") > behavior, and special cases (what will be, after MADV_COLLAPSE file > support) the only remaining callsite which *doesn't* care about > THP-pmds (ksm). The naming here is a little more meaningful than > "*raw", and IMHO more readable. > > > > > > { > > > > pgd_t *pgd; > > > > p4d_t *p4d; > > > > pud_t *pud; > > > > pmd_t *pmd = NULL; > > > > - pmd_t pmde; > > > > > > > > pgd = pgd_offset(mm, address); > > > > if (!pgd_present(*pgd)) > > > > @@ -788,6 +787,18 @@ pmd_t *mm_find_pmd(struct mm_struct *mm, unsigned long address) > > > > goto out; > > > > > > > > pmd = pmd_offset(pud, address); > > > > +out: > > > > + return pmd; > > > > +} > > > > + > > > > +pmd_t *mm_find_pmd(struct mm_struct *mm, unsigned long address) > > > > +{ > > > > + pmd_t pmde; > > > > + pmd_t *pmd; > > > > + > > > > + pmd = mm_find_pmd_raw(mm, address); > > > > + if (!pmd) > > > > + goto out; > > > > /* > > > > * Some THP functions use the sequence pmdp_huge_clear_flush(), set_pmd_at() > > > > * without holding anon_vma lock for write. So when looking for a > > > > -- > > > > 2.36.1.255.ge46751e96f-goog > > > >