linux-kernel - Re: [PATCH 1/1] mm: handle profiling for fake memory allocations during compaction

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Date: Tue, 2 Jul 2024 11:32:32 +0200
From: Vlastimil Babka <vbabka@...e.cz>
To: Suren Baghdasaryan <surenb@...gle.com>
Cc: akpm@...ux-foundation.org, kent.overstreet@...ux.dev,
 pasha.tatashin@...een.com, souravpanda@...gle.com, keescook@...omium.org,
 linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] mm: handle profiling for fake memory allocations
 during compaction

On 6/30/24 9:17 PM, Suren Baghdasaryan wrote:
> On Mon, Jun 17, 2024 at 1:33 AM Vlastimil Babka <vbabka@...e.cz> wrote:
>>
>> On 6/15/24 1:05 AM, Suren Baghdasaryan wrote:
>> > During compaction isolated free pages are marked allocated so that they
>> > can be split and/or freed. For that, post_alloc_hook() is used inside
>> > split_map_pages() and release_free_list(). split_map_pages() marks free
>> > pages allocated, splits the pages and then lets alloc_contig_range_noprof()
>> > free those pages. release_free_list() marks free pages and immediately
>>
>> Well in case of split_map_pages() only some of them end up freed, but most
>> should be used as migration targets. But we move the tags from the source
>> page during migration and unaccount the ones from the target (i.e. from the
>> instrumented post_alloc_hook() after this patch), right? So it should be ok,
>> just the description here is incomplete.
> 
> Sorry for the delay with replying, Vlastimil.
> Yes, you are correct. Some of these pages are not immediately freed
> but migrated and during migration the destination gets charged for
> them. As a result these new counters should still read 0 most of the
> time except for some intermediate states.
> I can amend the description if this is considered important.

The fix was merged to mainline already.