From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id F0EF913AA3E for ; Wed, 11 Sep 2024 12:00:43 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1726056047; cv=none; b=QeJt9YxxSDqlrOiD+bpxHzMTF8HuuRgDYkeyTACKUU0lttadeHrthsa1Bd/rDS92chY5DFzY7foo33P6gCl42qSqv+zk1Ie0+QXiyJ+DsHIyFVMI47fwHDvmbzHXirWuP2DZ8g/nlmeBdO0m3IZ/namM6iddTOK+UXYx7M0P0eQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1726056047; c=relaxed/simple; bh=hQguWJEfBWPr8JBEnyBpS+c5eZWedehS612Nu7YiuB8=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=hv7sA3PcW8JGvKX9P4mP5XgGLkOqWhZrHRaW73HgqJFFFim7wXILFDiuhL2kNUn4y46NVIoHkmEZVeZpD8grdqrQQgUQGk9rD4jKqE/zfjWPxCt1Rivuk2OqddYQZh3uvlYW45T3J15//2qrm9+NyqDwq++H2+25FeaWL8LR0GM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id A2D681007; Wed, 11 Sep 2024 05:01:12 -0700 (PDT) Received: from [10.162.40.31] (e116581.arm.com [10.162.40.31]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 8B2A13F66E; Wed, 11 Sep 2024 05:00:34 -0700 (PDT) Message-ID: <552e9b77-c1ea-4a60-8434-e360ca692f1f@arm.com> Date: Wed, 11 Sep 2024 17:30:27 +0530 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 1/2] mm: Abstract THP allocation To: David Hildenbrand , akpm@linux-foundation.org, willy@infradead.org, kirill.shutemov@linux.intel.com Cc: ryan.roberts@arm.com, anshuman.khandual@arm.com, catalin.marinas@arm.com, cl@gentwo.org, vbabka@suse.cz, mhocko@suse.com, apopple@nvidia.com, dave.hansen@linux.intel.com, will@kernel.org, baohua@kernel.org, jack@suse.cz, mark.rutland@arm.com, hughd@google.com, aneesh.kumar@kernel.org, yang@os.amperecomputing.com, peterx@redhat.com, ioworker0@gmail.com, jglisse@google.com, wangkefeng.wang@huawei.com, ziy@nvidia.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org References: <20240911065600.1002644-1-dev.jain@arm.com> <20240911065600.1002644-2-dev.jain@arm.com> Content-Language: en-US From: Dev Jain In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 9/11/24 14:57, David Hildenbrand wrote: > On 11.09.24 08:55, Dev Jain wrote: >> In preparation for the second patch, abstract away the THP allocation >> logic present in the create_huge_pmd() path, which corresponds to the >> faulting case when no page is present. >> >> There should be no functional change as a result of applying >> this patch. >> > > Hi, > >> Signed-off-by: Dev Jain >> --- >>   mm/huge_memory.c | 110 +++++++++++++++++++++++++++++------------------ >>   1 file changed, 67 insertions(+), 43 deletions(-) >> >> diff --git a/mm/huge_memory.c b/mm/huge_memory.c >> index 67c86a5d64a6..b96a1ff2bf40 100644 >> --- a/mm/huge_memory.c >> +++ b/mm/huge_memory.c >> @@ -943,47 +943,88 @@ unsigned long thp_get_unmapped_area(struct file >> *filp, unsigned long addr, >>   } >>   EXPORT_SYMBOL_GPL(thp_get_unmapped_area); >>   -static vm_fault_t __do_huge_pmd_anonymous_page(struct vm_fault *vmf, >> -            struct page *page, gfp_t gfp) >> +static struct folio *pmd_thp_fault_alloc(gfp_t gfp, struct >> vm_area_struct *vma, >> +                     unsigned long haddr, unsigned long addr) > > I suggest calling this something like "vma_alloc_anon_folio_pmd()"? > Then it's more consistent with vma_alloc_folio(). > > Also, likely we should just only pass in "addr" and calculate "haddr" > ourselves, it's cheap and reduces the number of function parameters. Makes sense, thanks. > >>   { >> -    struct vm_area_struct *vma = vmf->vma; >> -    struct folio *folio = page_folio(page); >> -    pgtable_t pgtable; >> -    unsigned long haddr = vmf->address & HPAGE_PMD_MASK; >> -    vm_fault_t ret = 0; >> +    const int order = HPAGE_PMD_ORDER; >> +    struct folio *folio = vma_alloc_folio(gfp, order, vma, haddr, >> true); >>   -    VM_BUG_ON_FOLIO(!folio_test_large(folio), folio); >> +    if (unlikely(!folio)) { >> +        count_vm_event(THP_FAULT_FALLBACK); >> +        count_mthp_stat(order, MTHP_STAT_ANON_FAULT_FALLBACK); >> +        goto out; >> +    } >>   +    VM_BUG_ON_FOLIO(!folio_test_large(folio), folio); >>       if (mem_cgroup_charge(folio, vma->vm_mm, gfp)) { >>           folio_put(folio); >>           count_vm_event(THP_FAULT_FALLBACK); >>           count_vm_event(THP_FAULT_FALLBACK_CHARGE); >> -        count_mthp_stat(HPAGE_PMD_ORDER, >> MTHP_STAT_ANON_FAULT_FALLBACK); >> -        count_mthp_stat(HPAGE_PMD_ORDER, >> MTHP_STAT_ANON_FAULT_FALLBACK_CHARGE); >> -        return VM_FAULT_FALLBACK; >> +        count_mthp_stat(order, MTHP_STAT_ANON_FAULT_FALLBACK); >> +        count_mthp_stat(order, MTHP_STAT_ANON_FAULT_FALLBACK_CHARGE); >> +        goto out; >>       } >>       folio_throttle_swaprate(folio, gfp); >>   -    pgtable = pte_alloc_one(vma->vm_mm); >> -    if (unlikely(!pgtable)) { >> -        ret = VM_FAULT_OOM; >> -        goto release; >> -    } >> - >> -    folio_zero_user(folio, vmf->address); >> +    folio_zero_user(folio, addr); >>       /* >>        * The memory barrier inside __folio_mark_uptodate makes sure that >>        * folio_zero_user writes become visible before the set_pmd_at() >>        * write. >>        */ >>       __folio_mark_uptodate(folio); >> +out: >> +    return folio; >> +} >> + >> +static void __pmd_thp_fault_success_stats(struct vm_area_struct *vma) >> +{ >> +    count_vm_event(THP_FAULT_ALLOC); >> +    count_mthp_stat(HPAGE_PMD_ORDER, MTHP_STAT_ANON_FAULT_ALLOC); >> +    count_memcg_event_mm(vma->vm_mm, THP_FAULT_ALLOC); >> +} > > Why isn't that moved into map_pmd_thp() > > Note that in this patch you do: > > map_pmd_thp(folio, vmf, vma, haddr); > spin_unlock(vmf->ptl); > __pmd_thp_fault_success_stats(vma); > > But in patch #2 > > map_pmd_thp(folio, vmf, vma, haddr); > __pmd_thp_fault_success_stats(vma); > goto unlock; > release: >     folio_put(folio); > unlock: >     spin_unlock(vmf->ptl); Yes, while writing it I knew about this inconsistency, but I wanted to reduce latency by dropping the lock before. But in do_huge_zero_wp_pmd(), I couldn't figure out a way to call the stat function after dropping the lock, without I guess, introducing too many labels and goto jumps and the like. In the current code, the lock gets dropped first. > > Please make that consistent, meaning: > > 1) Inline __pmd_thp_fault_success_stats() into map_pmd_thp(). No need > to have the separated out. > > 2) Either do the PTL unlocking in __pmd_thp_fault_success_stats() or in >    the caller. In the caller is likely easiest. Adjusting the counters >    should be cheap, if not we could revisit this later with real data. I will then call it in map_pmd_thp(), that is cleaner...I did find occurrences of these stat computations after taking the lock, for example, in do_swap_page(): count_vm_event(PGMAJFAULT) so I guess it should be alright. > >> + >> +static void map_pmd_thp(struct folio *folio, struct vm_fault *vmf, >> +            struct vm_area_struct *vma, unsigned long haddr) >> +{ >> +    pmd_t entry; >> + >> +    entry = mk_huge_pmd(&folio->page, vma->vm_page_prot); >> +    entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma); >> +    folio_add_new_anon_rmap(folio, vma, haddr, RMAP_EXCLUSIVE); >> +    folio_add_lru_vma(folio, vma); >> +    set_pmd_at(vma->vm_mm, haddr, vmf->pmd, entry); >> +    update_mmu_cache_pmd(vma, vmf->address, vmf->pmd); > > It's quite weird to see a mixture of haddr and vmf->address, and > likely this mixture is wrong or not not required. > > Looking at arc's update_mmu_cache_pmd() implementation, I cannot see > how passing in the unaligned address would do the right thing. But > maybe arc also doesn't trigger that code path ... who knows :) > > > Staring at some other update_mmu_cache_pmd() users, it's quite > inconsistent. Primarily only do_huge_pmd_numa_page() and > __do_huge_pmd_anonymous_page() use the unaligned address. The others > seem to use the aligned address ... as one would expect when modifying > a PMD. > > > I suggest to change this function to *not* pass in the vmf, and rename > it to something like: > > static void folio_map_anon_pmd(struct folio *folio, struct > vm_area_struct *vma, pmd_t *pmd, unsigned long haddr) > > Then use haddr also to do the update_mmu_cache_pmd(). The code I changed, already was passing vmf->address to update_mmu_cache_pmd(). I did not change any of the haddr and vmf->address semantics, so really can't comment on this. I agree with the name change; vmf will be required for set_pmd_at(vmf->pmd), so I should just pass pmd? > >> +    add_mm_counter(vma->vm_mm, MM_ANONPAGES, HPAGE_PMD_NR); >> +    mm_inc_nr_ptes(vma->vm_mm); >> +} >> + >> +static vm_fault_t __do_huge_pmd_anonymous_page(struct vm_fault *vmf) >> +{ >> +    struct vm_area_struct *vma = vmf->vma; >> +    struct folio *folio; >> +    pgtable_t pgtable; >> +    unsigned long haddr = vmf->address & HPAGE_PMD_MASK; >> +    vm_fault_t ret = 0; >> +    gfp_t gfp = vma_thp_gfp_mask(vma); > > Nit: While at it, try to use reverse christmas-tree where possible, > makes things more reasible. You could make haddr const. > > struct vm_area_struct *vma = vmf->vma; > unsigned long haddr = vmf->address & HPAGE_PMD_MASK; > gfp_t gfp = vma_thp_gfp_mask(vma); > struct folio *folio; > vm_fault_t ret = 0; Okay. > ... > >> + >> +    folio = pmd_thp_fault_alloc(gfp, vma, haddr, vmf->address); >> +    if (unlikely(!folio)) { >> +        ret = VM_FAULT_FALLBACK; >> +        goto release; >> +    } >> + >> +    pgtable = pte_alloc_one(vma->vm_mm); >> +    if (unlikely(!pgtable)) { >> +        ret = VM_FAULT_OOM; >> +        goto release; >> +    } >>         vmf->ptl = pmd_lock(vma->vm_mm, vmf->pmd); >> + > > Nit Unrelated change. Are you asking me to align this line with the below line? > >>       if (unlikely(!pmd_none(*vmf->pmd))) { >>           goto unlock_release; > >