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Thu, 20 Jun 2024 01:33:38 -0700 (PDT) MIME-Version: 1.0 References: <20240617231137.80726-1-21cnbao@gmail.com> <20240617231137.80726-3-21cnbao@gmail.com> In-Reply-To: From: Barry Song <21cnbao@gmail.com> Date: Thu, 20 Jun 2024 20:33:26 +1200 Message-ID: Subject: Re: [PATCH v2 2/3] mm: use folio_add_new_anon_rmap() if folio_test_anon(folio)==false To: David Hildenbrand Cc: akpm@linux-foundation.org, linux-mm@kvack.org, baolin.wang@linux.alibaba.com, chrisl@kernel.org, linux-kernel@vger.kernel.org, mhocko@suse.com, ryan.roberts@arm.com, shy828301@gmail.com, surenb@google.com, v-songbaohua@oppo.com, willy@infradead.org, ying.huang@intel.com, yosryahmed@google.com, yuzhao@google.com, Shuai Yuan Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam03 X-Rspam-User: X-Rspamd-Queue-Id: 057F840005 X-Stat-Signature: zahcjbbdj3ih9i4rh6yoom4mkq5y4w5u X-HE-Tag: 1718872418-990088 X-HE-Meta: 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 vIGccuOY ovdidiK2bCkHuVWvuFf+guGW1Ha/46YwpAYvBbWW29gHXZBuchixBWd20XvsdOdV8lqB69a72iPndL6gw5sim11Aw1kZEzKciqaFCfKA3cuF0B/Hnvv25IUHCorJF1N0mS90o6P3kfFn13NFfc4oybUFfAzyZJZTsARRSmQQZDATpQ9pnRdozNt0dT3fsFScnA0QKw1rUblX8VjA3HClVjdIZHt/EeqFSHRctN9GGSI3kYTJuhKAlCFFPIw0zVV8TQaoNtFI/GVhg++oqyJ0CHfDTcwXU45ln4WhHyrKyCA8WK+Gcuhs5xhu6Pf1ycoQlIYfUMv0gjNXna7pPWo9zwSVKBmTEPKPsG9H+AgpiACRSikoFC2Sjd7AA2zlSPJYW0G5pp6qlpgJ10D/C6aL27t+X1o6OcWS4PsUPjRqgvXOAUfs= 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: On Thu, Jun 20, 2024 at 7:46=E2=80=AFPM David Hildenbrand wrote: > > On 18.06.24 01:11, Barry Song wrote: > > From: Barry Song > > > > For the !folio_test_anon(folio) case, we can now invoke folio_add_new_a= non_rmap() > > with the rmap flags set to either EXCLUSIVE or non-EXCLUSIVE. This acti= on will > > suppress the VM_WARN_ON_FOLIO check within __folio_add_anon_rmap() whil= e initiating > > the process of bringing up mTHP swapin. > > > > static __always_inline void __folio_add_anon_rmap(struct folio *folio= , > > struct page *page, int nr_pages, struct vm_area_struc= t *vma, > > unsigned long address, rmap_t flags, enum rmap_level = level) > > { > > ... > > if (unlikely(!folio_test_anon(folio))) { > > VM_WARN_ON_FOLIO(folio_test_large(folio) && > > level !=3D RMAP_LEVEL_PMD, folio); > > } > > ... > > } > > > > It also improves the code=E2=80=99s readability. Currently, all new ano= nymous > > folios calling folio_add_anon_rmap_ptes() are order-0. This ensures > > that new folios cannot be partially exclusive; they are either entirely > > exclusive or entirely shared. > > > > Suggested-by: David Hildenbrand > > Signed-off-by: Barry Song > > Tested-by: Shuai Yuan > > --- > > mm/memory.c | 8 ++++++++ > > mm/swapfile.c | 13 +++++++++++-- > > 2 files changed, 19 insertions(+), 2 deletions(-) > > > > diff --git a/mm/memory.c b/mm/memory.c > > index 1f24ecdafe05..620654c13b2f 100644 > > --- a/mm/memory.c > > +++ b/mm/memory.c > > @@ -4339,6 +4339,14 @@ vm_fault_t do_swap_page(struct vm_fault *vmf) > > if (unlikely(folio !=3D swapcache && swapcache)) { > > folio_add_new_anon_rmap(folio, vma, address, RMAP_EXCLUSI= VE); > > folio_add_lru_vma(folio, vma); > > + } else if (!folio_test_anon(folio)) { > > + /* > > + * We currently only expect small !anon folios, for which= we now > > + * that they are either fully exclusive or fully shared. = If we > > + * ever get large folios here, we have to be careful. > > + */ > > + VM_WARN_ON_ONCE(folio_test_large(folio)); > > + folio_add_new_anon_rmap(folio, vma, address, rmap_flags); > > } else { > > folio_add_anon_rmap_ptes(folio, page, nr_pages, vma, addr= ess, > > rmap_flags); > > diff --git a/mm/swapfile.c b/mm/swapfile.c > > index ae1d2700f6a3..69efa1a57087 100644 > > --- a/mm/swapfile.c > > +++ b/mm/swapfile.c > > @@ -1908,8 +1908,17 @@ static int unuse_pte(struct vm_area_struct *vma,= pmd_t *pmd, > > VM_BUG_ON_FOLIO(folio_test_writeback(folio), folio); > > if (pte_swp_exclusive(old_pte)) > > rmap_flags |=3D RMAP_EXCLUSIVE; > > - > > - folio_add_anon_rmap_pte(folio, page, vma, addr, rmap_flag= s); > > + /* > > + * We currently only expect small !anon folios, for which= we now that > > + * they are either fully exclusive or fully shared. If we= ever get > > + * large folios here, we have to be careful. > > + */ > > + if (!folio_test_anon(folio)) { > > + VM_WARN_ON_ONCE(folio_test_large(folio)); > > (comment applies to both cases) > > Thinking about Hugh's comment, we should likely add here: > > VM_WARN_ON_FOLIO(!folio_test_locked(folio), folio); > > [the check we are removing from __folio_add_anon_rmap()] > > and document for folio_add_new_anon_rmap() in patch #1, that when > dealing with folios that might be mapped concurrently by others, the > folio lock must be held. I assume you mean something like the following for patch#1? diff --git a/mm/rmap.c b/mm/rmap.c index df1a43295c85..20986b25f1b2 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -1394,7 +1394,8 @@ void folio_add_anon_rmap_pmd(struct folio *folio, struct page *page, * * Like folio_add_anon_rmap_*() but must only be called on *new* folios. * This means the inc-and-test can be bypassed. - * The folio does not have to be locked. + * The folio doesn't necessarily need to be locked while it's exclusive unless two threads + * map it concurrently. However, the folio must be locked if it's shared. * * If the folio is pmd-mappable, it is accounted as a THP. */ @@ -1406,6 +1407,7 @@ void folio_add_new_anon_rmap(struct folio *folio, struct vm_area_struct *vma, int nr_pmdmapped =3D 0; VM_WARN_ON_FOLIO(folio_test_hugetlb(folio), folio); + VM_WARN_ON_FOLIO(!exclusive && !folio_test_locked(folio), folio); VM_BUG_ON_VMA(address < vma->vm_start || address + (nr << PAGE_SHIFT) > vma->vm_end, vma); __folio_set_swapbacked(folio); > > > + folio_add_new_anon_rmap(folio, vma, addr, rmap_fl= ags); > > + } else { > > + folio_add_anon_rmap_pte(folio, page, vma, addr, r= map_flags); > > + } > > } else { /* ksm created a completely new copy */ > > folio_add_new_anon_rmap(folio, vma, addr, RMAP_EXCLUSIVE)= ; > > folio_add_lru_vma(folio, vma); > > -- > Cheers, > > David / dhildenb >