linux-kernel - Re: [PATCH v5 1/2] mm: hugetlb: proc: add HugetlbPages field to /proc/PID/smaps

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Message-ID: <55ED5E6C.6000102@draigBrady.com>
Date:	Mon, 07 Sep 2015 10:52:44 +0100
From:	Pádraig Brady <P@...igBrady.com>
To:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	David Rientjes <rientjes@...gle.com>,
	Jörn Engel <joern@...estorage.com>,
	Mike Kravetz <mike.kravetz@...cle.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Naoya Horiguchi <nao.horiguchi@...il.com>
Subject: Re: [PATCH v5 1/2] mm: hugetlb: proc: add HugetlbPages field to /proc/PID/smaps

On 07/09/15 07:46, Naoya Horiguchi wrote:
> On Mon, Sep 07, 2015 at 02:23:44AM +0000, Horiguchi Naoya(堀口 直也) wrote:
>> On Mon, Sep 07, 2015 at 02:29:53AM +0100, Pádraig Brady wrote:
>>> On 20/08/15 09:26, Naoya Horiguchi wrote:
>>>> Currently /proc/PID/smaps provides no usage info for vma(VM_HUGETLB), which
>>>> is inconvenient when we want to know per-task or per-vma base hugetlb usage.
>>>> To solve this, this patch adds a new line for hugetlb usage like below:
>>>>
>>>>   Size:              20480 kB
>>>>   Rss:                   0 kB
>>>>   Pss:                   0 kB
>>>>   Shared_Clean:          0 kB
>>>>   Shared_Dirty:          0 kB
>>>>   Private_Clean:         0 kB
>>>>   Private_Dirty:         0 kB
>>>>   Referenced:            0 kB
>>>>   Anonymous:             0 kB
>>>>   AnonHugePages:         0 kB
>>>>   HugetlbPages:      18432 kB
>>>>   Swap:                  0 kB
>>>>   KernelPageSize:     2048 kB
>>>>   MMUPageSize:        2048 kB
>>>>   Locked:                0 kB
>>>>   VmFlags: rd wr mr mw me de ht
>>>>
>>>> Signed-off-by: Naoya Horiguchi <n-horiguchi@...jp.nec.com>
>>>> Acked-by: Joern Engel <joern@...fs.org>
>>>> Acked-by: David Rientjes <rientjes@...gle.com>
>>>> ---
>>>> v3 -> v4:
>>>> - suspend Acked-by tag because v3->v4 change is not trivial
>>>> - I stated in previous discussion that HugetlbPages line can contain page
>>>>   size info, but that's not necessary because we already have KernelPageSize
>>>>   info.
>>>> - merged documentation update, where the current documentation doesn't mention
>>>>   AnonHugePages, so it's also added.
>>>> ---
>>>>  Documentation/filesystems/proc.txt |  7 +++++--
>>>>  fs/proc/task_mmu.c                 | 29 +++++++++++++++++++++++++++++
>>>>  2 files changed, 34 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git v4.2-rc4/Documentation/filesystems/proc.txt v4.2-rc4_patched/Documentation/filesystems/proc.txt
>>>> index 6f7fafde0884..22e40211ef64 100644
>>>> --- v4.2-rc4/Documentation/filesystems/proc.txt
>>>> +++ v4.2-rc4_patched/Documentation/filesystems/proc.txt
>>>> @@ -423,6 +423,8 @@ Private_Clean:         0 kB
>>>>  Private_Dirty:         0 kB
>>>>  Referenced:          892 kB
>>>>  Anonymous:             0 kB
>>>> +AnonHugePages:         0 kB
>>>> +HugetlbPages:          0 kB
>>>>  Swap:                  0 kB
>>>>  KernelPageSize:        4 kB
>>>>  MMUPageSize:           4 kB
>>>> @@ -440,8 +442,9 @@ indicates the amount of memory currently marked as referenced or accessed.
>>>>  "Anonymous" shows the amount of memory that does not belong to any file.  Even
>>>>  a mapping associated with a file may contain anonymous pages: when MAP_PRIVATE
>>>>  and a page is modified, the file page is replaced by a private anonymous copy.
>>>> -"Swap" shows how much would-be-anonymous memory is also used, but out on
>>>> -swap.
>>>> +"AnonHugePages" shows the ammount of memory backed by transparent hugepage.
>>>> +"HugetlbPages" shows the ammount of memory backed by hugetlbfs page.
>>>> +"Swap" shows how much would-be-anonymous memory is also used, but out on swap.
>>>
>>> There is no distinction between "private" and "shared" in this "huge page" accounting right?
>>
>> Right for current version. And I think that private/shared distinction
>> gives some help.
>>
>>> Would it be possible to account for the huge pages in the {Private,Shared}_{Clean,Dirty} fields?
>>> Or otherwise split the huge page accounting into shared/private?
> 
> Sorry, I didn't catch you properly.
> I think that accounting for hugetlb pages should be done only with HugetlbPages
> or any other new field for hugetlb, in order not to break the behavior of existing
> fields. 

On a more general note I'd be inclined to just account
for hugetlb pages in Rss and {Private,Shared}_Dirty
and fix any tools that double count.

> So splitting HugetlbPages into shared/private looks good to me.

Yes this is the most compatible solution,
and will allow one to accurately determine
how much core mem a process is using.

thanks!
Pádraig.

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