From: Gregory CLEMENT <gregory.clement@bootlin.com>
To: Arnd Bergmann <arnd@arndb.de>
Cc: Thomas Petazzoni <thomas.petazzoni@bootlin.com>,
Russell King <linux@armlinux.org.uk>,
Linux ARM <linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH v2 4/6] ARM: mm: Aligned pte allocation to one page
Date: Fri, 12 Jun 2020 13:56:34 +0200 [thread overview]
Message-ID: <877dwc8pl9.fsf@FE-laptop> (raw)
In-Reply-To: <CAK8P3a2-g9ZmFiWJ_i4-0C6=WwzC1UjHGzY07w4y=0O1pHSX5Q@mail.gmail.com>
Arnd Bergmann <arnd@arndb.de> writes:
> On Thu, Jun 11, 2020 at 3:49 PM Gregory CLEMENT
> <gregory.clement@bootlin.com> wrote:
>>
>> In pte_offset_kernel() the pte_index macro is used. This macro makes
>> the assumption that the address is aligned to a page size.
>>
>> In arm_pte_allocation, the size allocated is the size needed for 512
>> entries. Actually this size was calculated to fit in a 4K page. When
>> using larger page, the size of the table allocated is no more
>> aligned which end to give a wrong physical address.
>>
>> The solution is to round up the allocation to a page size instead of
>> the exact size of the tables (which is 4KB). It allows to comply with
>> the assumption of pte_index() but the drawback is a waste of memory
>> for the early allocation if page size is bigger than 4KB.
>
> Have you considered increasing PTRS_PER_PTE instead to fill up
> a logical page instead? If that doesn't work, can you explain here
> why not?
Actually for this situation I didn't try to do better but it is only
used very early during the boot. Then I'm expecting that the allocation
is done though slab so with object at the exact size we need.
However you also pointed modifying PTRS_PER_PTE for the overall memory
consumption in the cover letter and in this case, it could worth
modifying it.
Gregory
>
> Arnd
--
Gregory Clement, Bootlin
Embedded Linux and Kernel engineering
http://bootlin.com
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next prev parent reply other threads:[~2020-06-12 11:56 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-11 13:49 [PATCH v2 0/6] ARM: Add support for large kernel page (from 8K to 64K) Gregory CLEMENT
2020-06-11 13:49 ` [PATCH v2 1/6] ARM: Use PAGE_SIZE for ELF_EXEC_PAGESIZE Gregory CLEMENT
2020-06-12 8:22 ` Arnd Bergmann
2020-06-12 8:35 ` Russell King - ARM Linux admin
2020-06-12 8:46 ` Arnd Bergmann
2020-06-12 8:50 ` Russell King - ARM Linux admin
2020-06-12 11:50 ` Catalin Marinas
2020-06-12 12:06 ` Gregory CLEMENT
2020-06-12 8:52 ` Gregory CLEMENT
2020-06-11 13:49 ` [PATCH v2 2/6] ARM: pagetable: prepare hardware page table to use large page Gregory CLEMENT
2020-06-11 13:49 ` [PATCH v2 3/6] ARM: Make the number of fix bitmap depend on the page size Gregory CLEMENT
2020-06-11 13:49 ` [PATCH v2 4/6] ARM: mm: Aligned pte allocation to one page Gregory CLEMENT
2020-06-12 8:37 ` Arnd Bergmann
2020-06-12 10:25 ` Catalin Marinas
2020-06-12 11:56 ` Gregory CLEMENT [this message]
2020-06-11 13:49 ` [PATCH v2 5/6] ARM: Add large kernel page support Gregory CLEMENT
2020-06-11 13:49 ` [PATCH v2 6/6] ARM: Add 64K page support at MMU level Gregory CLEMENT
2020-06-11 16:21 ` [PATCH v2 0/6] ARM: Add support for large kernel page (from 8K to 64K) Russell King - ARM Linux admin
2020-06-12 9:15 ` Gregory CLEMENT
2020-06-12 9:23 ` Arnd Bergmann
2020-06-12 12:21 ` Catalin Marinas
2020-06-12 12:49 ` Arnd Bergmann
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