linux-kernel - Re: [PATCH 2/2] alloc_tag: skip pgalloc_tag

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Message-Id: <20241226162315.cbf088cb28fe897bfe1b075b@linux-foundation.org>
Date: Thu, 26 Dec 2024 16:23:15 -0800
From: Andrew Morton <akpm@...ux-foundation.org>
To: Suren Baghdasaryan <surenb@...gle.com>
Cc: kent.overstreet@...ux.dev, yuzhao@...gle.com, 00107082@....com,
 quic_zhenhuah@...cinc.com, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH 2/2] alloc_tag: skip pgalloc_tag_swap if profiling is
 disabled

On Thu, 26 Dec 2024 15:07:39 -0800 Suren Baghdasaryan <surenb@...gle.com> wrote:

> On Thu, Dec 26, 2024 at 3:01 PM Andrew Morton <akpm@...ux-foundation.org> wrote:
> >
> > On Thu, 26 Dec 2024 13:16:39 -0800 Suren Baghdasaryan <surenb@...gle.com> wrote:
> >
> > > When memory allocation profiling is disabled, there is no need to swap
> > > allocation tags during migration. Skip it to avoid unnecessary overhead.
> > >
> > > Fixes: e0a955bf7f61 ("mm/codetag: add pgalloc_tag_copy()")
> > > Signed-off-by: Suren Baghdasaryan <surenb@...gle.com>
> > > Cc: stable@...r.kernel.org
> >
> > Are these changes worth backporting?  Some indication of how much
> > difference the patches make would help people understand why we're
> > proposing a backport.
> 
> The first patch ("alloc_tag: avoid current->alloc_tag manipulations
> when profiling is disabled") I think is worth backporting. It
> eliminates about half of the regression for slab allocations when
> profiling is disabled.

um, what regression?  The changelog makes no mention of this.  Please
send along a suitable Reported-by: and Closes: and a summary of the
benefits so that people can actually see what this patch does, and why.