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X-CSE-ConnectionGUID: BAn/YHLDSxSMYEvUfLZvyA== X-CSE-MsgGUID: I1dMkOfITdmelYyhLmLO7w== X-IronPort-AV: E=McAfee;i="6600,9927,11045"; a="12443197" X-IronPort-AV: E=Sophos;i="6.07,204,1708416000"; d="scan'208";a="12443197" Received: from fmviesa009.fm.intel.com ([10.60.135.149]) by orvoesa107.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 15 Apr 2024 20:19:49 -0700 X-CSE-ConnectionGUID: 3zaIK+QRSBm+gCqMmmVwsg== X-CSE-MsgGUID: 5967b8lWTRKxRf4cAmYCmw== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.07,204,1708416000"; d="scan'208";a="22190042" Received: from unknown (HELO yhuang6-desk2.ccr.corp.intel.com) ([10.238.208.55]) by fmviesa009-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 15 Apr 2024 20:19:45 -0700 From: "Huang, Ying" To: Barry Song <21cnbao@gmail.com> Cc: Khalid Aziz , akpm@linux-foundation.org, linux-mm@kvack.org, baolin.wang@linux.alibaba.com, chrisl@kernel.org, david@redhat.com, hanchuanhua@oppo.com, hannes@cmpxchg.org, hughd@google.com, kasong@tencent.com, ryan.roberts@arm.com, surenb@google.com, v-songbaohua@oppo.com, willy@infradead.org, xiang@kernel.org, yosryahmed@google.com, yuzhao@google.com, ziy@nvidia.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 4/5] mm: swap: entirely map large folios found in swapcache In-Reply-To: (Barry Song's message of "Tue, 16 Apr 2024 14:52:24 +1200") References: <20240409082631.187483-1-21cnbao@gmail.com> <20240409082631.187483-5-21cnbao@gmail.com> <87frvn2f89.fsf@yhuang6-desk2.ccr.corp.intel.com> <8734rm2gdj.fsf@yhuang6-desk2.ccr.corp.intel.com> <87y19e115l.fsf@yhuang6-desk2.ccr.corp.intel.com> Date: Tue, 16 Apr 2024 11:17:52 +0800 Message-ID: <87pluq0zdr.fsf@yhuang6-desk2.ccr.corp.intel.com> User-Agent: Gnus/5.13 (Gnus v5.13) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Rspam-User: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 1392140004 X-Stat-Signature: pgou4qioqf6h9acxmf1b5og151r1e41s X-HE-Tag: 1713237590-975797 X-HE-Meta: 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 j2bd5eDi aOFOFrHT286mAifyw0Vg1z1HXPVk+05I6Xh4OqdfNDzxhJxQUDIai1W540pD6YFrtBGbu08Q+B78yBWaRytx0kOSh1MuLySHxvYudefeHblBc1yqHsRjGfj4WlTma8u5pE59WLYL8XnYd/7qTVl4ZS4Ei0wbM+Qy5Aai2UwrC/yqmUdRFZME3e0aNOalv9YJ59SVd 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: List-Subscribe: List-Unsubscribe: Barry Song <21cnbao@gmail.com> writes: > On Tue, Apr 16, 2024 at 2:41=E2=80=AFPM Huang, Ying wrote: >> >> Barry Song <21cnbao@gmail.com> writes: >> >> > On Tue, Apr 16, 2024 at 2:27=E2=80=AFPM Huang, Ying wrote: >> >> >> >> >> >> Added Khalid for arch_do_swap_page(). >> >> >> >> Barry Song <21cnbao@gmail.com> writes: >> >> >> >> > On Mon, Apr 15, 2024 at 8:39=E2=80=AFPM Huang, Ying wrote: >> >> >> >> >> >> Barry Song <21cnbao@gmail.com> writes: >> >> >> >> [snip] >> >> >> >> >> >> >> >> > + bool any_swap_shared =3D false; >> >> >> > >> >> >> > if (!pte_unmap_same(vmf)) >> >> >> > goto out; >> >> >> > @@ -4137,6 +4141,35 @@ vm_fault_t do_swap_page(struct vm_fault *= vmf) >> >> >> > */ >> >> >> > vmf->pte =3D pte_offset_map_lock(vma->vm_mm, vmf->pmd, vmf= ->address, >> >> >> > &vmf->ptl); >> >> >> >> >> >> We should move pte check here. That is, >> >> >> >> >> >> if (unlikely(!vmf->pte || !pte_same(ptep_get(vmf->pte), vm= f->orig_pte))) >> >> >> goto out_nomap; >> >> >> >> >> >> This will simplify the situation for large folio. >> >> > >> >> > the plan is moving the whole code block >> >> > >> >> > if (start_pte && folio_test_large(folio) && folio_test_swapcache(fo= lio)) >> >> > >> >> > after >> >> > if (unlikely(!folio_test_uptodate(folio))) { >> >> > ret =3D VM_FAULT_SIGBUS; >> >> > goto out_nomap; >> >> > } >> >> > >> >> > though we couldn't be !folio_test_uptodate(folio)) for hitting >> >> > swapcache but it seems >> >> > logically better for future use. >> >> >> >> LGTM, Thanks! >> >> >> >> >> >> >> >> > + >> >> >> > + /* We hit large folios in swapcache */ >> >> >> >> >> >> The comments seems unnecessary because the code tells that already. >> >> >> >> >> >> > + if (start_pte && folio_test_large(folio) && folio_test_swa= pcache(folio)) { >> >> >> > + int nr =3D folio_nr_pages(folio); >> >> >> > + int idx =3D folio_page_idx(folio, page); >> >> >> > + unsigned long folio_start =3D vmf->address - idx *= PAGE_SIZE; >> >> >> > + unsigned long folio_end =3D folio_start + nr * PAG= E_SIZE; >> >> >> > + pte_t *folio_ptep; >> >> >> > + pte_t folio_pte; >> >> >> > + >> >> >> > + if (unlikely(folio_start < max(vmf->address & PMD_= MASK, vma->vm_start))) >> >> >> > + goto check_pte; >> >> >> > + if (unlikely(folio_end > pmd_addr_end(vmf->address= , vma->vm_end))) >> >> >> > + goto check_pte; >> >> >> > + >> >> >> > + folio_ptep =3D vmf->pte - idx; >> >> >> > + folio_pte =3D ptep_get(folio_ptep); >> >> >> >> >> >> It's better to construct pte based on fault PTE via generalizing >> >> >> pte_next_swp_offset() (may be pte_move_swp_offset()). Then we can= find >> >> >> inconsistent PTEs quicker. >> >> > >> >> > it seems your point is getting the pte of page0 by pte_next_swp_off= set() >> >> > unfortunately pte_next_swp_offset can't go back. on the other hand, >> >> > we have to check the real pte value of the 0nd entry right now beca= use >> >> > swap_pte_batch() only really reads pte from the 1st entry. it assum= es >> >> > pte argument is the real value for the 0nd pte entry. >> >> > >> >> > static inline int swap_pte_batch(pte_t *start_ptep, int max_nr, pte= _t pte) >> >> > { >> >> > pte_t expected_pte =3D pte_next_swp_offset(pte); >> >> > const pte_t *end_ptep =3D start_ptep + max_nr; >> >> > pte_t *ptep =3D start_ptep + 1; >> >> > >> >> > VM_WARN_ON(max_nr < 1); >> >> > VM_WARN_ON(!is_swap_pte(pte)); >> >> > VM_WARN_ON(non_swap_entry(pte_to_swp_entry(pte))); >> >> > >> >> > while (ptep < end_ptep) { >> >> > pte =3D ptep_get(ptep); >> >> > >> >> > if (!pte_same(pte, expected_pte)) >> >> > break; >> >> > >> >> > expected_pte =3D pte_next_swp_offset(expected_pte); >> >> > ptep++; >> >> > } >> >> > >> >> > return ptep - start_ptep; >> >> > } >> >> >> >> Yes. You are right. >> >> >> >> But we may check whether the pte of page0 is same as "vmf->orig_pte - >> >> folio_page_idx()" (fake code). >> > >> > right, that is why we are reading and checking PTE0 before calling >> > swap_pte_batch() >> > right now. >> > >> > folio_ptep =3D vmf->pte - idx; >> > folio_pte =3D ptep_get(folio_ptep); >> > if (!is_swap_pte(folio_pte) || non_swap_entry(pte_to_swp_entry(folio= _pte)) || >> > swap_pte_batch(folio_ptep, nr, folio_pte, &any_swap_shared) !=3D= nr) >> > goto check_pte; >> > >> > So, if I understand correctly, you're proposing that we should directl= y check >> > PTE0 in swap_pte_batch(). Personally, I don't have any objections to t= his idea. >> > However, I'd also like to hear the feedback from Ryan and David :-) >> >> I mean that we can replace >> >> !is_swap_pte(folio_pte) || non_swap_entry(pte_to_swp_entry(folio= _pte)) >> >> in above code with pte_same() with constructed expected first pte. > > Got it. It could be quite tricky, especially with considerations like > pte_swp_soft_dirty, pte_swp_exclusive, and pte_swp_uffd_wp. We might > require a helper function similar to pte_next_swp_offset() but capable of > moving both forward and backward. For instance: > > pte_move_swp_offset(pte_t pte, long delta) > > pte_next_swp_offset can insteadly call it by: > pte_move_swp_offset(pte, 1); > > Is it what you are proposing? Yes. Exactly. -- Best Regards, Huang, Ying >> >> >> >> >> You need to check the pte of page 0 anyway. >> >> >> >> >> >> >> >> > + if (!is_swap_pte(folio_pte) || non_swap_entry(pte_= to_swp_entry(folio_pte)) || >> >> >> > + swap_pte_batch(folio_ptep, nr, folio_pte, &any= _swap_shared) !=3D nr) >> >> >> > + goto check_pte; >> >> >> > + >> >> >> > + start_address =3D folio_start; >> >> >> > + start_pte =3D folio_ptep; >> >> >> > + nr_pages =3D nr; >> >> >> > + entry =3D folio->swap; >> >> >> > + page =3D &folio->page; >> >> >> > + } >> >> >> > + >> >> >> > +check_pte: >> >> >> > if (unlikely(!vmf->pte || !pte_same(ptep_get(vmf->pte), vm= f->orig_pte))) >> >> >> > goto out_nomap; >> >> >> > >> >> >> > @@ -4190,6 +4223,10 @@ vm_fault_t do_swap_page(struct vm_fault *= vmf) >> >> >> > */ >> >> >> > exclusive =3D false; >> >> >> > } >> >> >> > + >> >> >> > + /* Reuse the whole large folio iff all entries are= exclusive */ >> >> >> > + if (nr_pages > 1 && any_swap_shared) >> >> >> > + exclusive =3D false; >> >> >> > } >> >> >> > >> >> [snip] >> >> -- >> Best Regards, >> Huang, Ying