linux-kernel - Re: [PATCH 0/3] mm,TPP: Enable promotion of unmapped pagecache

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Message-ID: <875xrxhs5j.fsf@yhuang6-desk2.ccr.corp.intel.com>
Date: Mon, 19 Aug 2024 15:46:00 +0800
From: "Huang, Ying" <ying.huang@...el.com>
To: Gregory Price <gourry@...rry.net>
Cc: linux-mm@...ck.org,  linux-kernel@...r.kernel.org,
  akpm@...ux-foundation.org,  david@...hat.com,  nphamcs@...il.com,
  nehagholkar@...a.com,  abhishekd@...a.com, Johannes Weiner
 <hannes@...xchg.org>
Subject: Re: [PATCH 0/3] mm,TPP: Enable promotion of unmapped pagecache

Gregory Price <gourry@...rry.net> writes:

> Unmapped pagecache pages can be demoted to low-tier memory, but 
> they can only be promoted if a process maps the pages into the
> memory space (so that NUMA hint faults can be caught).  This can
> cause significant performance degradation as the pagecache ages
> and unmapped, cached files are accessed.
>
> This patch series enables the pagecache to request a promotion of
> a folio when it is accessed via the pagecache.
>
> We add a new `numa_hint_page_cache` counter in vmstat to capture
> information on when these migrations occur.

It appears that you will promote page cache page on the second access.
Do you have some better way to identify hot pages from the not-so-hot
pages?  How to balance between unmapped and mapped pages?  We have hot
page selection for hot pages.

[snip]

--
Best Regards,
Huang, Ying