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(p200300cbc715ee004e24cf8e3de08819.dip0.t-ipconnect.de. [2003:cb:c715:ee00:4e24:cf8e:3de0:8819]) by smtp.gmail.com with ESMTPSA id c19-20020a7bc853000000b004064288597bsm4411230wml.30.2023.10.06.13.08.20 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 06 Oct 2023 13:08:21 -0700 (PDT) Message-ID: <2f64809e-0d0d-cc61-71ac-8d9b072efc3a@redhat.com> Date: Fri, 6 Oct 2023 22:08:19 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.15.1 Subject: Re: [PATCH v6 6/9] mm: thp: Add "recommend" option for anon_orders Content-Language: en-US To: Ryan Roberts , Andrew Morton , Matthew Wilcox , Yin Fengwei , Yu Zhao , Catalin Marinas , Anshuman Khandual , Yang Shi , "Huang, Ying" , Zi Yan , Luis Chamberlain , Itaru Kitayama , "Kirill A. Shutemov" , John Hubbard , David Rientjes , Vlastimil Babka , Hugh Dickins Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org References: <20230929114421.3761121-1-ryan.roberts@arm.com> <20230929114421.3761121-7-ryan.roberts@arm.com> From: David Hildenbrand Organization: Red Hat In-Reply-To: <20230929114421.3761121-7-ryan.roberts@arm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 29.09.23 13:44, Ryan Roberts wrote: > In addition to passing a bitfield of folio orders to enable for THP, > allow the string "recommend" to be written, which has the effect of > causing the system to enable the orders preferred by the architecture > and by the mm. The user can see what these orders are by subsequently > reading back the file. > > Note that these recommended orders are expected to be static for a given > boot of the system, and so the keyword "auto" was deliberately not used, > as I want to reserve it for a possible future use where the "best" order > is chosen more dynamically at runtime. > > Recommended orders are determined as follows: > - PMD_ORDER: The traditional THP size > - arch_wants_pte_order() if implemented by the arch > - PAGE_ALLOC_COSTLY_ORDER: The largest order kept on per-cpu free list > > arch_wants_pte_order() can be overridden by the architecture if desired. > Some architectures (e.g. arm64) can coalsece TLB entries if a contiguous > set of ptes map physically contigious, naturally aligned memory, so this > mechanism allows the architecture to optimize as required. > > Here we add the default implementation of arch_wants_pte_order(), used > when the architecture does not define it, which returns -1, implying > that the HW has no preference. > > Signed-off-by: Ryan Roberts > --- > Documentation/admin-guide/mm/transhuge.rst | 4 ++++ > include/linux/pgtable.h | 13 +++++++++++++ > mm/huge_memory.c | 14 +++++++++++--- > 3 files changed, 28 insertions(+), 3 deletions(-) > > diff --git a/Documentation/admin-guide/mm/transhuge.rst b/Documentation/admin-guide/mm/transhuge.rst > index 732c3b2f4ba8..d6363d4efa3a 100644 > --- a/Documentation/admin-guide/mm/transhuge.rst > +++ b/Documentation/admin-guide/mm/transhuge.rst > @@ -187,6 +187,10 @@ pages (=16K if the page size is 4K). The example above enables order-9 > By enabling multiple orders, allocation of each order will be > attempted, highest to lowest, until a successful allocation is made. > If the PMD-order is unset, then no PMD-sized THPs will be allocated. > +It is also possible to enable the recommended set of orders, which > +will be optimized for the architecture and mm:: > + > + echo recommend >/sys/kernel/mm/transparent_hugepage/anon_orders > > The kernel will ignore any orders that it does not support so read the > file back to determine which orders are enabled:: > diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h > index af7639c3b0a3..0e110ce57cc3 100644 > --- a/include/linux/pgtable.h > +++ b/include/linux/pgtable.h > @@ -393,6 +393,19 @@ static inline void arch_check_zapped_pmd(struct vm_area_struct *vma, > } > #endif > > +#ifndef arch_wants_pte_order > +/* > + * Returns preferred folio order for pte-mapped memory. Must be in range [0, > + * PMD_ORDER) and must not be order-1 since THP requires large folios to be at > + * least order-2. Negative value implies that the HW has no preference and mm > + * will choose it's own default order. > + */ > +static inline int arch_wants_pte_order(void) > +{ > + return -1; > +} > +#endif > + > #ifndef __HAVE_ARCH_PTEP_GET_AND_CLEAR > static inline pte_t ptep_get_and_clear(struct mm_struct *mm, > unsigned long address, > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index bcecce769017..e2e2d3906a21 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -464,10 +464,18 @@ static ssize_t anon_orders_store(struct kobject *kobj, > int err; > int ret = count; > unsigned int orders; > + int arch; > > - err = kstrtouint(buf, 0, &orders); > - if (err) > - ret = -EINVAL; > + if (sysfs_streq(buf, "recommend")) { > + arch = max(arch_wants_pte_order(), PAGE_ALLOC_COSTLY_ORDER); > + orders = BIT(arch); > + orders |= BIT(PAGE_ALLOC_COSTLY_ORDER); > + orders |= BIT(PMD_ORDER); > + } else { > + err = kstrtouint(buf, 0, &orders); > + if (err) > + ret = -EINVAL; > + } > > if (ret > 0) { > orders &= THP_ORDERS_ALL_ANON; :/ don't really like that. Regarding my proposal, one could have something like that in an "auto" setting for the "enabled" value, or a "recommended" setting [not sure]. -- Cheers, David / dhildenb