linux-kernel - Re: [PATCH] docs: update THP admin guide about non-tmpfs filesystem support

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Message-ID: <midpuwlrt6tllgk2lpcntariyyt7msp7uyv32syfwne2p662yg@ux2zb7flcam3>
Date: Thu, 3 Apr 2025 20:21:19 +0200
From: "Pankaj Raghav (Samsung)" <kernel@...kajraghav.com>
To: David Hildenbrand <david@...hat.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, 
	Jonathan Corbet <corbet@....net>, linux-kernel@...r.kernel.org, willy@...radead.org, 
	linux-mm@...ck.org, da.gomez@...nel.org, mcgrof@...nel.org, gost.dev@...sung.com, 
	linux-doc@...r.kernel.org, Pankaj Raghav <p.raghav@...sung.com>
Subject: Re: [PATCH] docs: update THP admin guide about non-tmpfs filesystem
 support

> >      in the examples below we presume that the basic page size is 4K and
> > @@ -463,6 +463,10 @@ fields for each mapping. (Note that AnonHugePages only applies to traditional
> >   PMD-sized THP for historical reasons and should have been called
> >   AnonHugePmdMapped).
> > +The number of PMD-sized transparent huge pages currently used by
> > +filesystem data (page cache) is available by reading the FileHugePages field
> > +in ``/proc/meminfo``.
> > +
> 
> These changed look good. Do we also want to talk about FilePmdMapped?
> (PMD-sized THPs in the page cache that are mapped in to user space using a
> PMD ?)

I am a bit new to this subsystem, and it took some time to wrap around all
the different terminology used :)

But sure, I will add a new commit to talk about FilePmdMapped. I can
give it a shot with what I understand about FilePmdMapped, but please feel
free to add your input.

> 
> Do we have to distinguish it from below? (shmem also uses the page cache)
> 
> >   The number of file transparent huge pages mapped to userspace is available
> >   by reading ShmemPmdMapped and ShmemHugePages fields in ``/proc/meminfo``.
> >   To identify what applications are mapping file transparent huge pages, it
> 
> Previously here, but: this reads rather odd. "file transparent huge pages".
> "PMD-sized THPs specific to shmem are tracked separately ..." ?
> 

I totally agree. Reading "file transparent huge pages" confused me even
more. I will fold these changes as well.

Thanks, David.

--
Pankaj