linux-kernel - Re: [RFC PATCH 16/20] famfs: Add fault counters

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Date: Sat, 24 Feb 2024 03:59:11 +0000
From: Matthew Wilcox <willy@...radead.org>
To: Dan Williams <dan.j.williams@...el.com>
Cc: Dave Hansen <dave.hansen@...el.com>, John Groves <John@...ves.net>,
	John Groves <jgroves@...ron.com>, Jonathan Corbet <corbet@....net>,
	Vishal Verma <vishal.l.verma@...el.com>,
	Dave Jiang <dave.jiang@...el.com>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>,
	linux-cxl@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	nvdimm@...ts.linux.dev, john@...alactic.com,
	Dave Chinner <david@...morbit.com>,
	Christoph Hellwig <hch@...radead.org>, dave.hansen@...ux.intel.com,
	gregory.price@...verge.com
Subject: Re: [RFC PATCH 16/20] famfs: Add fault counters

On Fri, Feb 23, 2024 at 03:50:33PM -0800, Dan Williams wrote:
> Certainly something like that would have satisified this sanity test use
> case. I will note that mm_account_fault() would need some help to figure
> out the size of the page table entry that got installed. Maybe
> extensions to vm_fault_reason to add VM_FAULT_P*D? That compliments
> VM_FAULT_FALLBACK to indicate whether, for example, the fallback went
> from PUD to PMD, or all the way back to PTE.

ugh, no, it's more complicated than that.  look at the recent changes to
set_ptes().  we can now install PTEs of many different sizes, depending
on the architecture.  someday i look forward to supporting all the page
sizes on parisc (4k, 16k, 64k, 256k, ... 4G)