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Fri, 15 May 2020 13:50:40 +0000 (UTC) Received: from [10.36.114.77] (ovpn-114-77.ams2.redhat.com [10.36.114.77]) by smtp.corp.redhat.com (Postfix) with ESMTP id E60BF614E7; Fri, 15 May 2020 13:50:37 +0000 (UTC) Subject: Re: mm/memory.c: Add update local tlb for smp race To: Bibo Mao , Andrew Morton Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-mips@vger.kernel.org References: <1589439021-17005-1-git-send-email-maobibo@loongson.cn> From: David Hildenbrand Autocrypt: addr=david@redhat.com; prefer-encrypt=mutual; keydata= mQINBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABtCREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT6JAlgEEwEIAEICGwMFCQlmAYAGCwkIBwMCBhUI AgkKCwQWAgMBAh4BAheAFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl3pImkCGQEACgkQTd4Q 9wD/g1o+VA//SFvIHUAvul05u6wKv/pIR6aICPdpF9EIgEU448g+7FfDgQwcEny1pbEzAmiw zAXIQ9H0NZh96lcq+yDLtONnXk/bEYWHHUA014A1wqcYNRY8RvY1+eVHb0uu0KYQoXkzvu+s Dncuguk470XPnscL27hs8PgOP6QjG4jt75K2LfZ0eAqTOUCZTJxA8A7E9+XTYuU0hs7QVrWJ jQdFxQbRMrYz7uP8KmTK9/Cnvqehgl4EzyRaZppshruKMeyheBgvgJd5On1wWq4ZUV5PFM4x II3QbD3EJfWbaJMR55jI9dMFa+vK7MFz3rhWOkEx/QR959lfdRSTXdxs8V3zDvChcmRVGN8U Vo93d1YNtWnA9w6oCW1dnDZ4kgQZZSBIjp6iHcA08apzh7DPi08jL7M9UQByeYGr8KuR4i6e RZI6xhlZerUScVzn35ONwOC91VdYiQgjemiVLq1WDDZ3B7DIzUZ4RQTOaIWdtXBWb8zWakt/ ztGhsx0e39Gvt3391O1PgcA7ilhvqrBPemJrlb9xSPPRbaNAW39P8ws/UJnzSJqnHMVxbRZC Am4add/SM+OCP0w3xYss1jy9T+XdZa0lhUvJfLy7tNcjVG/sxkBXOaSC24MFPuwnoC9WvCVQ ZBxouph3kqc4Dt5X1EeXVLeba+466P1fe1rC8MbcwDkoUo65Ag0EVcufkQEQAOfX3n0g0fZz Bgm/S2zF/kxQKCEKP8ID+Vz8sy2GpDvveBq4H2Y34XWsT1zLJdvqPI4af4ZSMxuerWjXbVWb T6d4odQIG0fKx4F8NccDqbgHeZRNajXeeJ3R7gAzvWvQNLz4piHrO/B4tf8svmRBL0ZB5P5A 2uhdwLU3NZuK22zpNn4is87BPWF8HhY0L5fafgDMOqnf4guJVJPYNPhUFzXUbPqOKOkL8ojk CXxkOFHAbjstSK5Ca3fKquY3rdX3DNo+EL7FvAiw1mUtS+5GeYE+RMnDCsVFm/C7kY8c2d0G NWkB9pJM5+mnIoFNxy7YBcldYATVeOHoY4LyaUWNnAvFYWp08dHWfZo9WCiJMuTfgtH9tc75 7QanMVdPt6fDK8UUXIBLQ2TWr/sQKE9xtFuEmoQGlE1l6bGaDnnMLcYu+Asp3kDT0w4zYGsx 5r6XQVRH4+5N6eHZiaeYtFOujp5n+pjBaQK7wUUjDilPQ5QMzIuCL4YjVoylWiBNknvQWBXS lQCWmavOT9sttGQXdPCC5ynI+1ymZC1ORZKANLnRAb0NH/UCzcsstw2TAkFnMEbo9Zu9w7Kv AxBQXWeXhJI9XQssfrf4Gusdqx8nPEpfOqCtbbwJMATbHyqLt7/oz/5deGuwxgb65pWIzufa N7eop7uh+6bezi+rugUI+w6DABEBAAGJAiUEGAECAA8FAlXLn5ECGwwFCQlmAYAACgkQTd4Q 9wD/g1qA6w/+M+ggFv+JdVsz5+ZIc6MSyGUozASX+bmIuPeIecc9UsFRatc91LuJCKMkD9Uv GOcWSeFpLrSGRQ1Z7EMzFVU//qVs6uzhsNk0RYMyS0B6oloW3FpyQ+zOVylFWQCzoyyf227y GW8HnXunJSC+4PtlL2AY4yZjAVAPLK2l6mhgClVXTQ/S7cBoTQKP+jvVJOoYkpnFxWE9pn4t H5QIFk7Ip8TKr5k3fXVWk4lnUi9MTF/5L/mWqdyIO1s7cjharQCstfWCzWrVeVctpVoDfJWp 4LwTuQ5yEM2KcPeElLg5fR7WB2zH97oI6/Ko2DlovmfQqXh9xWozQt0iGy5tWzh6I0JrlcxJ ileZWLccC4XKD1037Hy2FLAjzfoWgwBLA6ULu0exOOdIa58H4PsXtkFPrUF980EEibUp0zFz GotRVekFAceUaRvAj7dh76cToeZkfsjAvBVb4COXuhgX6N4pofgNkW2AtgYu1nUsPAo+NftU CxrhjHtLn4QEBpkbErnXQyMjHpIatlYGutVMS91XTQXYydCh5crMPs7hYVsvnmGHIaB9ZMfB njnuI31KBiLUks+paRkHQlFcgS2N3gkRBzH7xSZ+t7Re3jvXdXEzKBbQ+dC3lpJB0wPnyMcX FOTT3aZT7IgePkt5iC/BKBk3hqKteTnJFeVIT7EC+a6YUFg= Organization: Red Hat GmbH Message-ID: Date: Fri, 15 May 2020 15:50:37 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 MIME-Version: 1.0 In-Reply-To: <1589439021-17005-1-git-send-email-maobibo@loongson.cn> Content-Type: text/plain; charset=utf-8 Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Content-Transfer-Encoding: quoted-printable 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 14.05.20 08:50, Bibo Mao wrote: > If there are two threads hitting page fault at the address, one > thread updates pte entry and local tlb, the other thread can update > local tlb also, rather than give up and let page fault happening > again. Let me suggest "mm/memory: optimize concurrent page faults at same address If two threads concurrently fault at the same address, the thread that won the race updates the PTE and its local TLB. For now, the other thread gives up, simply does nothing, and continues. It could happen that this second thread triggers another fault, whereby it only updates its local TLB while handling the fault. Instead of triggering another fault, let's directly update the local TLB of the second thread. " If I got the intention of this patch correctly. Are there any performance numbers to support this patch? (I can't say too much about the correctness and/or usefulness of this pat= ch) >=20 > modified: mm/memory.c This does not belong into a patch description. > Signed-off-by: Bibo Mao > --- > mm/memory.c | 30 ++++++++++++++++++++++-------- > 1 file changed, 22 insertions(+), 8 deletions(-) >=20 > diff --git a/mm/memory.c b/mm/memory.c > index f703fe8..3a741ce 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -2436,11 +2436,10 @@ static inline bool cow_user_page(struct page *d= st, struct page *src, > if (!likely(pte_same(*vmf->pte, vmf->orig_pte))) { > /* > * Other thread has already handled the fault > - * and we don't need to do anything. If it's > - * not the case, the fault will be triggered > - * again on the same address. > + * and update local tlb only > */ > ret =3D false; > + update_mmu_cache(vma, addr, vmf->pte); > goto pte_unlock; > } > =20 > @@ -2463,8 +2462,9 @@ static inline bool cow_user_page(struct page *dst= , struct page *src, > vmf->pte =3D pte_offset_map_lock(mm, vmf->pmd, addr, &vmf->ptl); > locked =3D true; > if (!likely(pte_same(*vmf->pte, vmf->orig_pte))) { > - /* The PTE changed under us. Retry page fault. */ > + /* The PTE changed under us. update local tlb */ > ret =3D false; > + update_mmu_cache(vma, addr, vmf->pte); > goto pte_unlock; > } > =20 > @@ -2704,6 +2704,7 @@ static vm_fault_t wp_page_copy(struct vm_fault *v= mf) > } > flush_cache_page(vma, vmf->address, pte_pfn(vmf->orig_pte)); > entry =3D mk_pte(new_page, vma->vm_page_prot); > + entry =3D pte_mkyoung(entry); > entry =3D maybe_mkwrite(pte_mkdirty(entry), vma); > /* > * Clear the pte entry and flush it first, before updating the > @@ -2752,6 +2753,7 @@ static vm_fault_t wp_page_copy(struct vm_fault *v= mf) > new_page =3D old_page; > page_copied =3D 1; > } else { > + update_mmu_cache(vma, vmf->address, vmf->pte); > mem_cgroup_cancel_charge(new_page, memcg, false); > } > =20 > @@ -2812,6 +2814,7 @@ vm_fault_t finish_mkwrite_fault(struct vm_fault *= vmf) > * pte_offset_map_lock. > */ > if (!pte_same(*vmf->pte, vmf->orig_pte)) { > + update_mmu_cache(vmf->vma, vmf->address, vmf->pte); > pte_unmap_unlock(vmf->pte, vmf->ptl); > return VM_FAULT_NOPAGE; > } > @@ -2936,6 +2939,7 @@ static vm_fault_t do_wp_page(struct vm_fault *vmf= ) > vmf->pte =3D pte_offset_map_lock(vma->vm_mm, vmf->pmd, > vmf->address, &vmf->ptl); > if (!pte_same(*vmf->pte, vmf->orig_pte)) { > + update_mmu_cache(vma, vmf->address, vmf->pte); > unlock_page(vmf->page); > pte_unmap_unlock(vmf->pte, vmf->ptl); > put_page(vmf->page); > @@ -3341,8 +3345,10 @@ static vm_fault_t do_anonymous_page(struct vm_fa= ult *vmf) > vma->vm_page_prot)); > vmf->pte =3D pte_offset_map_lock(vma->vm_mm, vmf->pmd, > vmf->address, &vmf->ptl); > - if (!pte_none(*vmf->pte)) > + if (!pte_none(*vmf->pte)) { > + update_mmu_cache(vma, vmf->address, vmf->pte); > goto unlock; > + } > ret =3D check_stable_address_space(vma->vm_mm); > if (ret) > goto unlock; > @@ -3373,13 +3379,16 @@ static vm_fault_t do_anonymous_page(struct vm_f= ault *vmf) > __SetPageUptodate(page); > =20 > entry =3D mk_pte(page, vma->vm_page_prot); > + entry =3D pte_mkyoung(entry); > if (vma->vm_flags & VM_WRITE) > entry =3D pte_mkwrite(pte_mkdirty(entry)); > =20 > vmf->pte =3D pte_offset_map_lock(vma->vm_mm, vmf->pmd, vmf->address, > &vmf->ptl); > - if (!pte_none(*vmf->pte)) > + if (!pte_none(*vmf->pte)) { > + update_mmu_cache(vma, vmf->address, vmf->pte); > goto release; > + } > =20 > ret =3D check_stable_address_space(vma->vm_mm); > if (ret) > @@ -3646,11 +3655,14 @@ vm_fault_t alloc_set_pte(struct vm_fault *vmf, = struct mem_cgroup *memcg, > } > =20 > /* Re-check under ptl */ > - if (unlikely(!pte_none(*vmf->pte))) > + if (unlikely(!pte_none(*vmf->pte))) { > + update_mmu_cache(vma, vmf->address, vmf->pte); > return VM_FAULT_NOPAGE; > + } > =20 > flush_icache_page(vma, page); > entry =3D mk_pte(page, vma->vm_page_prot); > + entry =3D pte_mkyoung(entry); > if (write) > entry =3D maybe_mkwrite(pte_mkdirty(entry), vma); > /* copy-on-write page */ > @@ -4224,8 +4236,10 @@ static vm_fault_t handle_pte_fault(struct vm_fau= lt *vmf) > vmf->ptl =3D pte_lockptr(vmf->vma->vm_mm, vmf->pmd); > spin_lock(vmf->ptl); > entry =3D vmf->orig_pte; > - if (unlikely(!pte_same(*vmf->pte, entry))) > + if (unlikely(!pte_same(*vmf->pte, entry))) { > + update_mmu_cache(vmf->vma, vmf->address, vmf->pte); > goto unlock; > + } > if (vmf->flags & FAULT_FLAG_WRITE) { > if (!pte_write(entry)) > return do_wp_page(vmf); >=20 --=20 Thanks, David / dhildenb