linux-kernel - Re: [PATCH] mm/page_owner.c: allow page_owner with given start

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Date:   Wed, 27 Jul 2022 12:59:36 +0200
From:   "Vlastimil Babka (SUSE)" <vbabka@...nel.org>
To:     Kassey Li <quic_yingangl@...cinc.com>,
        Matthew Wilcox <willy@...radead.org>
Cc:     akpm@...ux-foundation.org, minchan@...nel.org,
        iamjoonsoo.kim@....com, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, quic_guptap@...cinc.com
Subject: Re: [PATCH] mm/page_owner.c: allow page_owner with given
 start_pfn/count

On 7/27/22 09:44, Kassey Li wrote:
> 
> 
> On 7/26/2022 10:03 PM, Vlastimil Babka (SUSE) wrote:
>> On 7/25/22 10:39, Kassey Li wrote:
>>> hi, Matthew:
>>>      sorry for the delay, I just started to learn how to upstream patch, and
>>> setup my Thunderbird with plain text only.
>>>      you are right, two users will cause problem here.
>>>      the uses case is dump CMA area to understand the page usage in a given
>>> cma pool. 2nd, dump whole memory page owner is very time cost, mostly our
>>> android device has 8G memory now.
>>>      I will research and check again, if you have more idea on this , please
>>> kindly to share.
>>
>> You could try employing lseek() to specify the start pfn, and as for end
>> pfn, the process can just stop reading and close when it has seen enough?
> 
> lseek is a good idea.
> read_page_owner start with below
>     pfn = min_low_pfn + *ppos;
> so we need to export the min_low_pfn to user then decide the ppos to seek.
> (my_cma.base_pfn - min_low_pfn) is the ppos we want to set.

Hm could we just pfn = *ppos and then anything below min_low_pfn is skipped
internally? So we don't need to teach userspace min_low_pfn.

> is there concern to export min_low_pfn  ?
> or use a mutex lock for my previous debugfs version patch ?
> 
>>
>>> BR
>>> Kassey
>>>
>>> On 7/22/2022 11:38 PM, Matthew Wilcox wrote:
>>>> On Fri, Jul 22, 2022 at 11:08:10PM +0800, Kassey Li wrote:
>>>>> by default, page_owner iterates all page from min_low_pfn to
>>>>> max_pfn, this cost too much time if we want an alternative pfn range.
>>>>>
>>>>> with this patch it allows user to set pfn range to dump the page_onwer.
>>>>
>>>> This is a really bad UI.  If two users try to do different ranges at the
>>>> same time, it'll go wrong.  What use cases are you actually trying to
>>>> solve?
>>>
>>