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[142.68.25.194]) by smtp.gmail.com with ESMTPSA id w14-20020a0cef8e000000b0062df95d7ef6sm3777254qvr.115.2023.06.27.10.01.11 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 27 Jun 2023 10:01:12 -0700 (PDT) Received: from jgg by wakko with local (Exim 4.95) (envelope-from ) id 1qEC3z-008yOA-DP; Tue, 27 Jun 2023 14:01:11 -0300 Date: Tue, 27 Jun 2023 14:01:11 -0300 From: Jason Gunthorpe To: Hugh Dickins Cc: Andrew Morton , Gerald Schaefer , Vasily Gorbik , Mike Kravetz , Mike Rapoport , "Kirill A. Shutemov" , Matthew Wilcox , David Hildenbrand , Suren Baghdasaryan , Qi Zheng , Yang Shi , Mel Gorman , Peter Xu , Peter Zijlstra , Will Deacon , Yu Zhao , Alistair Popple , Ralph Campbell , Ira Weiny , Steven Price , SeongJae Park , Lorenzo Stoakes , Huang Ying , Naoya Horiguchi , Christophe Leroy , Zack Rusin , Axel Rasmussen , Anshuman Khandual , Pasha Tatashin , Miaohe Lin , Minchan Kim , Christoph Hellwig , Song Liu , Thomas Hellstrom , Russell King , "David Sc. Miller" , Michael Ellerman , "Aneesh Kumar K.V" , Heiko Carstens , Christian Borntraeger , Claudio Imbrenda , Alexander Gordeev , Jann Horn , Vishal Moola , Vlastimil Babka , linux-arm-kernel@lists.infradead.org, sparclinux@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH v2 05/12] powerpc: add pte_free_defer() for pgtables sharing page Message-ID: References: <54cb04f-3762-987f-8294-91dafd8ebfb0@google.com> <5cd9f442-61da-4c3d-eca-b7f44d22aa5f@google.com> <2ad8b6cf-692a-ff89-ecc-586c20c5e07f@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Queue-Id: 3C6071A013F X-Rspam-User: X-Rspamd-Server: rspam11 X-Stat-Signature: 56snsh7pmn6bsigsx7a1tr8im5uirrjb X-HE-Tag: 1687885273-51013 X-HE-Meta: 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 qkeWPpNi 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 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 Wed, Jun 21, 2023 at 07:36:11PM -0700, Hugh Dickins wrote: > [PATCH v3 05/12] powerpc: add pte_free_defer() for pgtables sharing page > > Add powerpc-specific pte_free_defer(), to free table page via call_rcu(). > pte_free_defer() will be called inside khugepaged's retract_page_tables() > loop, where allocating extra memory cannot be relied upon. This precedes > the generic version to avoid build breakage from incompatible pgtable_t. > > This is awkward because the struct page contains only one rcu_head, but > that page may be shared between PTE_FRAG_NR pagetables, each wanting to > use the rcu_head at the same time. But powerpc never reuses a fragment > once it has been freed: so mark the page Active in pte_free_defer(), > before calling pte_fragment_free() directly; and there call_rcu() to > pte_free_now() when last fragment is freed and the page is PageActive. > > Suggested-by: Jason Gunthorpe > Signed-off-by: Hugh Dickins > --- > arch/powerpc/include/asm/pgalloc.h | 4 ++++ > arch/powerpc/mm/pgtable-frag.c | 29 ++++++++++++++++++++++++++--- > 2 files changed, 30 insertions(+), 3 deletions(-) > > diff --git a/arch/powerpc/include/asm/pgalloc.h b/arch/powerpc/include/asm/pgalloc.h > index 3360cad78ace..3a971e2a8c73 100644 > --- a/arch/powerpc/include/asm/pgalloc.h > +++ b/arch/powerpc/include/asm/pgalloc.h > @@ -45,6 +45,10 @@ static inline void pte_free(struct mm_struct *mm, pgtable_t ptepage) > pte_fragment_free((unsigned long *)ptepage, 0); > } > > +/* arch use pte_free_defer() implementation in arch/powerpc/mm/pgtable-frag.c */ > +#define pte_free_defer pte_free_defer > +void pte_free_defer(struct mm_struct *mm, pgtable_t pgtable); > + > /* > * Functions that deal with pagetables that could be at any level of > * the table need to be passed an "index_size" so they know how to > diff --git a/arch/powerpc/mm/pgtable-frag.c b/arch/powerpc/mm/pgtable-frag.c > index 20652daa1d7e..0c6b68130025 100644 > --- a/arch/powerpc/mm/pgtable-frag.c > +++ b/arch/powerpc/mm/pgtable-frag.c > @@ -106,6 +106,15 @@ pte_t *pte_fragment_alloc(struct mm_struct *mm, int kernel) > return __alloc_for_ptecache(mm, kernel); > } > > +static void pte_free_now(struct rcu_head *head) > +{ > + struct page *page; > + > + page = container_of(head, struct page, rcu_head); > + pgtable_pte_page_dtor(page); > + __free_page(page); > +} > + > void pte_fragment_free(unsigned long *table, int kernel) > { > struct page *page = virt_to_page(table); > @@ -115,8 +124,22 @@ void pte_fragment_free(unsigned long *table, int kernel) > > BUG_ON(atomic_read(&page->pt_frag_refcount) <= 0); > if (atomic_dec_and_test(&page->pt_frag_refcount)) { > - if (!kernel) > - pgtable_pte_page_dtor(page); > - __free_page(page); > + if (kernel) > + __free_page(page); > + else if (TestClearPageActive(page)) > + call_rcu(&page->rcu_head, pte_free_now); > + else > + pte_free_now(&page->rcu_head); > } > } > + > +#ifdef CONFIG_TRANSPARENT_HUGEPAGE > +void pte_free_defer(struct mm_struct *mm, pgtable_t pgtable) > +{ > + struct page *page; > + > + page = virt_to_page(pgtable); > + SetPageActive(page); > + pte_fragment_free((unsigned long *)pgtable, 0); > +} > +#endif /* CONFIG_TRANSPARENT_HUGEPAGE */ Yes, this makes sense to me, very simple.. I always for get these details but atomic_dec_and_test() is a release? So the SetPageActive is guarenteed to be visible in another thread that reaches 0? Thanks, Jason