From: Ryan Roberts <ryan.roberts@arm.com>
To: Yu Zhao <yuzhao@google.com>, "Yin, Fengwei" <fengwei.yin@intel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Matthew Wilcox <willy@infradead.org>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
David Hildenbrand <david@redhat.com>,
Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will@kernel.org>,
Anshuman Khandual <anshuman.khandual@arm.com>,
Yang Shi <shy828301@gmail.com>,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH v2 3/5] mm: Default implementation of arch_wants_pte_order()
Date: Tue, 4 Jul 2023 14:23:20 +0100 [thread overview]
Message-ID: <dd9ea461-df2d-afe1-a67c-c73ac1cb96b4@arm.com> (raw)
In-Reply-To: <6d389825-1fc0-5c16-7858-2290fd632682@arm.com>
On 04/07/2023 13:36, Ryan Roberts wrote:
> On 04/07/2023 04:59, Yu Zhao wrote:
>> On Mon, Jul 3, 2023 at 9:02 PM Yu Zhao <yuzhao@google.com> wrote:
>>>
>>> On Mon, Jul 3, 2023 at 8:23 PM Yin, Fengwei <fengwei.yin@intel.com> wrote:
>>>>
>>>>
>>>>
>>>> On 7/3/2023 9:53 PM, Ryan Roberts wrote:
>>>>> arch_wants_pte_order() can be overridden by the arch to return the
>>>>> preferred folio order for pte-mapped memory. This is useful as some
>>>>> architectures (e.g. arm64) can coalesce TLB entries when the physical
>>>>> memory is suitably contiguous.
>>>>>
>>>>> The first user for this hint will be FLEXIBLE_THP, which aims to
>>>>> allocate large folios for anonymous memory to reduce page faults and
>>>>> other per-page operation costs.
>>>>>
>>>>> Here we add the default implementation of the function, used when the
>>>>> architecture does not define it, which returns the order corresponding
>>>>> to 64K.
>>>>>
>>>>> Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
>>>>> ---
>>>>> include/linux/pgtable.h | 13 +++++++++++++
>>>>> 1 file changed, 13 insertions(+)
>>>>>
>>>>> diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
>>>>> index a661a17173fa..f7e38598f20b 100644
>>>>> --- a/include/linux/pgtable.h
>>>>> +++ b/include/linux/pgtable.h
>>>>> @@ -13,6 +13,7 @@
>>>>> #include <linux/errno.h>
>>>>> #include <asm-generic/pgtable_uffd.h>
>>>>> #include <linux/page_table_check.h>
>>>>> +#include <linux/sizes.h>
>>>>>
>>>>> #if 5 - defined(__PAGETABLE_P4D_FOLDED) - defined(__PAGETABLE_PUD_FOLDED) - \
>>>>> defined(__PAGETABLE_PMD_FOLDED) != CONFIG_PGTABLE_LEVELS
>>>>> @@ -336,6 +337,18 @@ static inline bool arch_has_hw_pte_young(void)
>>>>> }
>>>>> #endif
>>>>>
>>>>> +#ifndef arch_wants_pte_order
>>>>> +/*
>>>>> + * Returns preferred folio order for pte-mapped memory. Must be in range [0,
>>>>> + * PMD_SHIFT-PAGE_SHIFT) and must not be order-1 since THP requires large folios
>>>>> + * to be at least order-2.
>>>>> + */
>>>>> +static inline int arch_wants_pte_order(struct vm_area_struct *vma)
>>>>> +{
>>>>> + return ilog2(SZ_64K >> PAGE_SHIFT);
>>>> Default value which is not related with any silicon may be: PAGE_ALLOC_COSTLY_ORDER?
>>>>
>>>> Also, current pcp list support cache page with order 0...PAGE_ALLOC_COSTLY_ORDER, 9.
>>>> If the pcp could cover the page, the pressure to zone lock will be reduced by pcp.
>>>
>>> The value of PAGE_ALLOC_COSTLY_ORDER is reasonable but again it's a
>>> s/w policy not a h/w preference. Besides, I don't think we can include
>>> mmzone.h in pgtable.h.
>>
>> I think we can make a compromise:
>> 1. change the default implementation of arch_has_hw_pte_young() to return 0, and
>> 2. in memory.c, we can try PAGE_ALLOC_COSTLY_ORDER for archs that
>> don't override arch_has_hw_pte_young(), or if its return value is too
>> large to fit.
>> This should also take care of the regression, right?
>
> I think you are suggesting that we use 0 as a sentinel which we then translate
> to PAGE_ALLOC_COSTLY_ORDER? I already have a max_anon_folio_order() function in
> memory.c (actually it is currently a macro defined as arch_wants_pte_order()).
>
> So it would become (I'll talk about the vma concern separately in the thread
> where you raised it):
>
> static inline int max_anon_folio_order(struct vm_area_struct *vma)
> {
> int order = arch_wants_pte_order(vma);
>
> return order ? order : PAGE_ALLOC_COSTLY_ORDER;
> }
>
> Correct?
Actually, I'm not sure its a good idea to default to a fixed order. If running
on an arch with big base pages (e.g. powerpc with 64K pages?), that will soon
add up to a big chunk of memory, which could be wasteful?
PAGE_ALLOC_COSTLY_ORDER = 3 so with 64K base page, that 512K. Is that a concern?
Wouldn't it be better to define this as an absolute size? Or even the min of
PAGE_ALLOC_COSTLY_ORDER and an absolute size?
>
> I don't see how it fixes the regression (assume you're talking about
> Speedometer) though? On arm64 arch_wants_pte_order() will still be returning
> order-4.
>
next prev parent reply other threads:[~2023-07-04 13:23 UTC|newest]
Thread overview: 84+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-07-03 13:53 [PATCH v2 0/5] variable-order, large folios for anonymous memory Ryan Roberts
2023-07-03 13:53 ` [PATCH v2 1/5] mm: Non-pmd-mappable, large folios for folio_add_new_anon_rmap() Ryan Roberts
2023-07-03 19:05 ` Yu Zhao
2023-07-04 2:13 ` Yin, Fengwei
2023-07-04 11:19 ` Ryan Roberts
2023-07-04 2:14 ` Yin, Fengwei
2023-07-03 13:53 ` [PATCH v2 2/5] mm: Allow deferred splitting of arbitrary large anon folios Ryan Roberts
2023-07-07 8:21 ` Huang, Ying
2023-07-07 9:42 ` Ryan Roberts
2023-07-10 5:37 ` Huang, Ying
2023-07-10 8:29 ` Ryan Roberts
2023-07-10 9:01 ` Huang, Ying
2023-07-10 9:39 ` Ryan Roberts
2023-07-11 1:56 ` Huang, Ying
2023-07-03 13:53 ` [PATCH v2 3/5] mm: Default implementation of arch_wants_pte_order() Ryan Roberts
2023-07-03 19:50 ` Yu Zhao
2023-07-04 13:20 ` Ryan Roberts
2023-07-05 2:07 ` Yu Zhao
2023-07-05 9:11 ` Ryan Roberts
2023-07-05 17:24 ` Yu Zhao
2023-07-05 18:01 ` Ryan Roberts
2023-07-06 19:33 ` Matthew Wilcox
2023-07-07 10:00 ` Ryan Roberts
2023-07-04 2:22 ` Yin, Fengwei
2023-07-04 3:02 ` Yu Zhao
2023-07-04 3:59 ` Yu Zhao
2023-07-04 5:22 ` Yin, Fengwei
2023-07-04 5:42 ` Yu Zhao
2023-07-04 12:36 ` Ryan Roberts
2023-07-04 13:23 ` Ryan Roberts [this message]
2023-07-05 1:40 ` Yu Zhao
2023-07-05 1:23 ` Yu Zhao
2023-07-05 2:18 ` Yin Fengwei
2023-07-03 13:53 ` [PATCH v2 4/5] mm: FLEXIBLE_THP for improved performance Ryan Roberts
2023-07-03 15:51 ` kernel test robot
2023-07-03 16:01 ` kernel test robot
2023-07-04 1:35 ` Yu Zhao
2023-07-04 14:08 ` Ryan Roberts
2023-07-04 23:47 ` Yu Zhao
2023-07-04 3:45 ` Yin, Fengwei
2023-07-04 14:20 ` Ryan Roberts
2023-07-04 23:35 ` Yin Fengwei
2023-07-04 23:57 ` Matthew Wilcox
2023-07-05 9:54 ` Ryan Roberts
2023-07-05 12:08 ` Matthew Wilcox
2023-07-07 8:01 ` Huang, Ying
2023-07-07 9:52 ` Ryan Roberts
2023-07-07 11:29 ` David Hildenbrand
2023-07-07 13:57 ` Matthew Wilcox
2023-07-07 14:07 ` David Hildenbrand
2023-07-07 15:13 ` Ryan Roberts
2023-07-07 16:06 ` David Hildenbrand
2023-07-07 16:22 ` Ryan Roberts
2023-07-07 19:06 ` David Hildenbrand
2023-07-10 8:41 ` Ryan Roberts
2023-07-10 3:03 ` Huang, Ying
2023-07-10 8:55 ` Ryan Roberts
2023-07-10 9:18 ` Huang, Ying
2023-07-10 9:25 ` Ryan Roberts
2023-07-11 0:48 ` Huang, Ying
2023-07-10 2:49 ` Huang, Ying
2023-07-03 13:53 ` [PATCH v2 5/5] arm64: mm: Override arch_wants_pte_order() Ryan Roberts
2023-07-03 20:02 ` Yu Zhao
2023-07-04 2:18 ` [PATCH v2 0/5] variable-order, large folios for anonymous memory Yu Zhao
2023-07-04 6:22 ` Yin, Fengwei
2023-07-04 7:11 ` Yu Zhao
2023-07-04 15:36 ` Ryan Roberts
2023-07-04 23:52 ` Yin Fengwei
2023-07-05 0:21 ` Yu Zhao
2023-07-05 10:16 ` Ryan Roberts
2023-07-05 19:00 ` Yu Zhao
2023-07-05 19:38 ` David Hildenbrand
2023-07-06 8:02 ` Ryan Roberts
2023-07-07 11:40 ` David Hildenbrand
2023-07-07 13:12 ` Matthew Wilcox
2023-07-07 13:24 ` David Hildenbrand
2023-07-10 10:07 ` Ryan Roberts
2023-07-10 16:57 ` Matthew Wilcox
2023-07-10 16:53 ` Zi Yan
2023-07-19 15:49 ` Ryan Roberts
2023-07-19 16:05 ` Zi Yan
2023-07-19 18:37 ` Ryan Roberts
2023-07-11 21:11 ` Luis Chamberlain
2023-07-11 21:59 ` Matthew Wilcox
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