lkml.org 
[lkml]   [2021]   [Oct]   [7]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
SubjectRe: [PATCH v10 3/3] mm: add anonymous vma name refcounting
From
On 10/7/21 11:50, Suren Baghdasaryan wrote:
...
>>>>>>>>>> I believe Pavel meant something as simple as
>>>>>>>>>> $ YOUR_FILE=$YOUR_IDS_DIR/my_string_name
>>>>>>>>>> $ touch $YOUR_FILE
>>>>>>>>>> $ stat -c %i $YOUR_FILE
>>>>>>>
>>>>>>> Ah, ok, now I understand the proposal. Thanks for the clarification!
>>>>>>> So, this would use filesystem as a directory for inode->name mappings.
>>>>>>> One rough edge for me is that the consumer would still need to parse
>>>>>>> /proc/$pid/maps and convert [anon:inode] into [anon:name] instead of
>>>>>>> just dumping the content for the user. Would it be acceptable if we
>>>>>>> require the ID provided by prctl() to always be a valid inode and
>>>>>>> show_map_vma() would do the inode-to-filename conversion when
>>>>>>> generating maps/smaps files? I know that inode->dentry is not
>>>>>>> one-to-one mapping but we can simply output the first dentry name.
>>>>>>> WDYT?
>>>>>>
>>>>>> No. You do not want to dictate any particular way of the mapping. The
>>>>>> above is just one way to do that without developing any actual mapping
>>>>>> yourself. You just use a filesystem for that. Kernel doesn't and
>>>>>> shouldn't understand the meaning of those numbers. It has no business in
>>>>>> that.
>>>>>>
>>>>>> In a way this would be pushing policy into the kernel.
>>>>>
>>>>> I can see your point. Any other ideas on how to prevent tools from
>>>>> doing this id-to-name conversion themselves?
>>>>
>>>> I really fail to understand why you really want to prevent them from that.
>>>> Really, the whole thing is just a cookie that kernel maintains for memory
>>>> mappings so that two parties can understand what the meaning of that
>>>> mapping is from a higher level. They both have to agree on the naming
>>>> but the kernel shouldn't dictate any specific convention because the
>>>> kernel _doesn't_ _care_. These things are not really anything actionable
>>>> for the kernel. It is just a metadata.
>>>
>>> The desire is for one of these two parties to be a human who can get
>>> the data and use it as is without additional conversions.
>>> /proc/$pid/maps could report FD numbers instead of pathnames, which
>>> could be converted to pathnames in userspace. However we do not do
>>> that because pathnames are more convenient for humans to identify a
>>> specific resource. Same logic applies here IMHO.
>>
>> Yes, please. It really seems like the folks that are interested in this
>> feature want strings. (I certainly do.) For those not interested in the
>> feature, it sounds like a CONFIG to keep it away would be sufficient.
>> Can we just move forward with that?
>
> Would love to if others are ok with this.
>

If this doesn't get accepted, then another way forward would to continue
the ideas above to their logical conclusion, and create a new file system:
vma-fs. Like debug-fs and other special file systems, similar policy and
motivation. Also protected by a CONFIG option.

Actually this seems at least as natural as the procfs approach, especially
given the nature of these strings, which feel more like dir+file names, than
simple strings.

thanks,
--
John Hubbard
NVIDIA

\
 
 \ /
  Last update: 2021-10-07 21:04    [W:0.179 / U:0.724 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site