Re: [PATCH 4/4] mm: proc/pid/smaps_rollup: convert to single value seq_file

[Vlastimil Babka]

On 07/26/2018 06:26 PM, Alexey Dobriyan wrote:
> On Wed, Jul 25, 2018 at 08:53:53AM +0200, Vlastimil Babka wrote:
>> I moved the reply to this thread since the "added to -mm tree"
>> notification Alexey replied to in <20180724182908.GD27053@avx2> has
>> reduced CC list and is not linked to the patch postings.
>>
>> On 07/24/2018 08:29 PM, Alexey Dobriyan wrote:
>>> On Mon, Jul 23, 2018 at 04:55:48PM -0700, akpm@xxxxxxxxxxxxxxxxxxxx wrote:
>>>> The patch titled
>>>>      Subject: mm: /proc/pid/smaps_rollup: convert to single value seq_file
>>>> has been added to the -mm tree.  Its filename is
>>>>      mm-proc-pid-smaps_rollup-convert-to-single-value-seq_file.patch
>>>
>>>> Subject: mm: /proc/pid/smaps_rollup: convert to single value seq_file
>>>>
>>>> The /proc/pid/smaps_rollup file is currently implemented via the
>>>> m_start/m_next/m_stop seq_file iterators shared with the other maps files,
>>>> that iterate over vma's.  However, the rollup file doesn't print anything
>>>> for each vma, only accumulate the stats.
>>>
>>> What I don't understand why keep seq_ops then and not do all the work in
>>> ->show hook.  Currently /proc/*/smaps_rollup is at ~500 bytes so with
>>> minimum 1 page seq buffer, no buffer resizing is possible.
>>
>> Hmm IIUC seq_file also provides the buffer and handles feeding the data
>> from there to the user process, which might have called read() with a smaller
>> buffer than that. So I would rather not avoid the seq_file infrastructure.
>> Or you're saying it could be converted to single_open()? Maybe, with more work.
> 
> Prefereably yes.

OK here it is. Sending as a new patch instead of delta, as that's easier
to review - the delta is significant. Line stats wise it's the same.
Again a bit less boilerplate thans to no special seq_ops, a bit more
copy/paste in the open and release functions. But I guess it's better
overall.

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