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Date: Tue, 13 Feb 2024 11:03:07 +0900
From: Byungchul Park <byungchul@sk.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	kernel_team@skhynix.com, ying.huang@intel.com, namit@vmware.com,
	vernhao@tencent.com, mgorman@techsingularity.net, hughd@google.com,
	willy@infradead.org, david@redhat.com, peterz@infradead.org,
	luto@kernel.org, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de,
	dave.hansen@linux.intel.com, rjgolo@gmail.com
Subject: Re: [RESEND PATCH v7 6/8] mm: Add APIs to free a folio directly to
 the buddy bypassing pcp
Message-ID: <20240213020307.GC4147@system.software.com>
References: <20240208062608.44351-1-byungchul@sk.com>
 <20240208062608.44351-7-byungchul@sk.com>
 <20240208124919.a0e1707fefc29c2f4213e509@linux-foundation.org>
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On Thu, Feb 08, 2024 at 12:49:19PM -0800, Andrew Morton wrote:
> On Thu,  8 Feb 2024 15:26:06 +0900 Byungchul Park <byungchul@sk.com> wrote:
> 
> > This is a preparation for migrc mechanism that frees folios at a better
> 
> The term "migrc" appears in various places but I don't think we're told
> what is actually means?
> 
> > time later, rather than the moment migrating folios. The folios freed by
> > migrc are too old to keep in pcp.
> 
> How do we define "too old" and what causes you to believe this is the case?

Migrc defers folio_put() for source folios of migration that would be
unlikely used and frees a bunch of folios at once later. However, it
pollutes pcp, which means fresher folios might get free_pcppages_bulk()ed
and makes the effort to keep the best amount of pcp get unstable. So I
didn't want to make this situation happen.

	Byungchul