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Mon, 20 Apr 2020 12:46:19 +0000 Received: from b03ledav002.gho.boulder.ibm.com (b03ledav002.gho.boulder.ibm.com [9.17.130.233]) by b03cxnp08028.gho.boulder.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 03KCkHha62325118 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Mon, 20 Apr 2020 12:46:17 GMT Received: from b03ledav002.gho.boulder.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 6E2D113604F; Mon, 20 Apr 2020 12:46:17 +0000 (GMT) Received: from b03ledav002.gho.boulder.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 9ED39136059; Mon, 20 Apr 2020 12:46:13 +0000 (GMT) Received: from skywalker.ibmuc.com (unknown [9.199.51.43]) by b03ledav002.gho.boulder.ibm.com (Postfix) with ESMTP; Mon, 20 Apr 2020 12:46:13 +0000 (GMT) From: "Aneesh Kumar K.V" To: linuxppc-dev@lists.ozlabs.org, mpe@ellerman.id.au, linux-mm@kvack.org, linux-kernel@vger.kernel.org, kvm-ppc@vger.kernel.org Cc: npiggin@gmail.com, paulus@ozlabs.org, leonardo@linux.ibm.com, kirill@shutemov.name, "Aneesh Kumar K.V" Subject: [PATCH v3 20/22] powerpc/mm/book3s64: Avoid sending IPI on clearing PMD Date: Mon, 20 Apr 2020 18:14:32 +0530 Message-Id: <20200420124434.47330-21-aneesh.kumar@linux.ibm.com> X-Mailer: git-send-email 2.25.3 In-Reply-To: <20200420124434.47330-1-aneesh.kumar@linux.ibm.com> References: <20200420124434.47330-1-aneesh.kumar@linux.ibm.com> MIME-Version: 1.0 X-TM-AS-GCONF: 00 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.138,18.0.676 definitions=2020-04-20_03:2020-04-20,2020-04-20 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 bulkscore=0 priorityscore=1501 spamscore=0 lowpriorityscore=0 adultscore=0 impostorscore=0 mlxscore=0 malwarescore=0 suspectscore=0 mlxlogscore=962 clxscore=1015 phishscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2003020000 definitions=main-2004200107 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: Now that all the lockless page table walk is careful w.r.t the PTE address returned, we can now revert commit: 13bd817bb884 ("powerpc/thp: Serialize pmd clear against a linux p= age table walk.") We also drop the equivalent IPI from other pte updates routines. We still= keep IPI in hash pmdp collapse and that is to take care of parallel hash page = table insert. The radix pmdp collapse flush can possibly be removed once I am s= ure generic code doesn't have the any expectations around parallel gup walk. This speeds up Qemu guest RAM del/unplug time as below 128 core, 496GB guest: Without patch: munmap start: timer =3D 13162 ms, PID=3D7684 munmap finish: timer =3D 95312 ms, PID=3D7684 - delta =3D 82150 ms With patch: munmap start: timer =3D 196449 ms, PID=3D6681 munmap finish: timer =3D 196488 ms, PID=3D6681 - delta =3D 39ms Signed-off-by: Aneesh Kumar K.V --- arch/powerpc/mm/book3s64/hash_pgtable.c | 11 ----------- arch/powerpc/mm/book3s64/pgtable.c | 8 -------- arch/powerpc/mm/book3s64/radix_pgtable.c | 19 +++++++------------ 3 files changed, 7 insertions(+), 31 deletions(-) diff --git a/arch/powerpc/mm/book3s64/hash_pgtable.c b/arch/powerpc/mm/bo= ok3s64/hash_pgtable.c index 64733b9cb20a..64ca375278dc 100644 --- a/arch/powerpc/mm/book3s64/hash_pgtable.c +++ b/arch/powerpc/mm/book3s64/hash_pgtable.c @@ -363,17 +363,6 @@ pmd_t hash__pmdp_huge_get_and_clear(struct mm_struct= *mm, * hash fault look at them. */ memset(pgtable, 0, PTE_FRAG_SIZE); - /* - * Serialize against find_current_mm_pte variants which does lock-less - * lookup in page tables with local interrupts disabled. For huge pages - * it casts pmd_t to pte_t. Since format of pte_t is different from - * pmd_t we want to prevent transit from pmd pointing to page table - * to pmd pointing to huge page (and back) while interrupts are disable= d. - * We clear pmd to possibly replace it with page table pointer in - * different code paths. So make sure we wait for the parallel - * find_curren_mm_pte to finish. - */ - serialize_against_pte_lookup(mm); return old_pmd; } =20 diff --git a/arch/powerpc/mm/book3s64/pgtable.c b/arch/powerpc/mm/book3s6= 4/pgtable.c index e0bb69c616e4..127325ead505 100644 --- a/arch/powerpc/mm/book3s64/pgtable.c +++ b/arch/powerpc/mm/book3s64/pgtable.c @@ -109,14 +109,6 @@ pmd_t pmdp_invalidate(struct vm_area_struct *vma, un= signed long address, =20 old_pmd =3D pmd_hugepage_update(vma->vm_mm, address, pmdp, _PAGE_PRESEN= T, _PAGE_INVALID); flush_pmd_tlb_range(vma, address, address + HPAGE_PMD_SIZE); - /* - * This ensures that generic code that rely on IRQ disabling - * to prevent a parallel THP split work as expected. - * - * Marking the entry with _PAGE_INVALID && ~_PAGE_PRESENT requires - * a special case check in pmd_access_permitted. - */ - serialize_against_pte_lookup(vma->vm_mm); return __pmd(old_pmd); } =20 diff --git a/arch/powerpc/mm/book3s64/radix_pgtable.c b/arch/powerpc/mm/b= ook3s64/radix_pgtable.c index 8f9edf07063a..dfb9fe92aea8 100644 --- a/arch/powerpc/mm/book3s64/radix_pgtable.c +++ b/arch/powerpc/mm/book3s64/radix_pgtable.c @@ -962,7 +962,13 @@ pmd_t radix__pmdp_collapse_flush(struct vm_area_stru= ct *vma, unsigned long addre pmd =3D *pmdp; pmd_clear(pmdp); =20 - /*FIXME!! Verify whether we need this kick below */ + /* + * pmdp collapse_flush need to ensure that there are no parallel gup + * walk after this call. This is needed so that we can have stable + * page ref count when collapsing a page. We don't allow a collapse pag= e + * if we have gup taken on the page. We can ensure that by sending IPI + * because gup walk happens with IRQ disabled. + */ serialize_against_pte_lookup(vma->vm_mm); =20 radix__flush_tlb_collapsed_pmd(vma->vm_mm, address); @@ -1023,17 +1029,6 @@ pmd_t radix__pmdp_huge_get_and_clear(struct mm_str= uct *mm, =20 old =3D radix__pmd_hugepage_update(mm, addr, pmdp, ~0UL, 0); old_pmd =3D __pmd(old); - /* - * Serialize against find_current_mm_pte which does lock-less - * lookup in page tables with local interrupts disabled. For huge pages - * it casts pmd_t to pte_t. Since format of pte_t is different from - * pmd_t we want to prevent transit from pmd pointing to page table - * to pmd pointing to huge page (and back) while interrupts are disable= d. - * We clear pmd to possibly replace it with page table pointer in - * different code paths. So make sure we wait for the parallel - * find_current_mm_pte to finish. - */ - serialize_against_pte_lookup(mm); return old_pmd; } =20 --=20 2.25.3