linux-kernel - Re: [PATCH v3 22/22] mm/mshare: charge fault handling allocations to the mshare owner

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Message-ID: <3752d094-e754-4453-b404-75d92de3e364@oracle.com>
Date: Mon, 8 Sep 2025 12:21:11 -0700
From: Anthony Yznaga <anthony.yznaga@...cle.com>
To: David Hildenbrand <david@...hat.com>, linux-mm@...ck.org
Cc: akpm@...ux-foundation.org, andreyknvl@...il.com, arnd@...db.de,
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Subject: Re: [PATCH v3 22/22] mm/mshare: charge fault handling allocations to
 the mshare owner



On 9/8/25 11:50 AM, David Hildenbrand wrote:
> On 20.08.25 03:04, Anthony Yznaga wrote:
>> When handling a fault in an mshare range, redirect charges for page
>> tables and other allocations to the mshare owner rather than the
>> current task.
>>
> 
> That looks rather weird. I would have thought there would be an easy way 
> to query the mshare owner for a given mshare mapping, and if the current 
> MM corresponds to that owner you know that you are running in the owner 
> context.
> 
> Of course, we could have a helper like is_mshare_owner(mapping, current) 
> or sth like that.
> 

I'm not quite following you. Charges for newly faulted pages will be 
automatically directed to the mshare owner because the mshare mm will 
have its mm_owner field pointing to the owner. On the other hand, 
allocations for page table pages are handled differently. 
GFP_PGTABLE_USER causes the accounting to go through 
__memcg_kmem_charge_page() which will charge them to the memcg for the 
current task unless unless current->active_memcg is set to point to 
another memcg.