Re: Better active/inactive list balancing

[Mtrr Patt <mtrr.patt@gmail.com>]

Hi Johannes,
On 05/01/2013 11:21 PM, Johannes Weiner wrote:
> Hi Wanpeng Li / Ni zhan Chen / Jaegeuk Hanse / Simon Jeons / Will Huck
> / Ric Mason / Sam Ben / Mtrr Patt!
>
> On Wed, May 01, 2013 at 02:55:53PM +0800, Mtrr Patt wrote:
>> Hi Johannes,
>> On 05/01/2013 12:32 AM, Johannes Weiner wrote:
>>> On Sat, Apr 27, 2013 at 02:20:54PM +0800, Mtrr Patt wrote:
>>>> cc linux-mm
>>>>
>>>> On 04/27/2013 02:19 PM, Mtrr Patt wrote:
>>>>> Hi Johannes,
>>>>>
>>>>> http://lwn.net/Articles/495543/
>>>>>
>>>>> This link said that "When active pages are considered for
>>>>> eviction, they are first moved to the inactive list and unmapped
>>>> >from the address space of the process(es) using them. Thus, once a
>>>>> page moves to the inactive list, any attempt to reference it will
>>>>> generate a page fault; this "soft fault" will cause the page to be
>>>>> removed back to the active list."
>>>>>
>>>>> Why I can't find the codes unmap during page moved from active
>>>>> list to inactive list?
>>> Most architectures have the hardware track the referenced bit in the
>>> page tables, but some don't.  For them, page_referenced_one() will
>>> mark the mapping read-only when clearing the referenced/young bit and
>>> the page fault handler will set the bit manually.
>> Thanks for your response. ;-) So the article is not against more
>> common case, isn't it?
> It's about the generic/theoretic case I guess, not the optimized
> implementation.
>
>>> When mapped pages reach the end of the inactive list and have that bit
>>> set, they get activated, see page_check_references().
>> It seems that the page should trigger page fault twice and
>> page_check_references can active it.
> The first one brings it into memory (major fault), the second one sets
> the referenced bit (minor fault or set by mmu).  Then it gets
> activated.  That is the case for mmap accessed pages.
>
> Buffered IO (read/write syscalls) enters the kernel anyway, so we
> activate the pages right then and there with mark_page_accessed().

Thanks for your explaination. Why you say hi to other guys, confuse me! ;-)

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