linux-kernel - Re: [PATCH] perf: map pages in advance

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Message-ID: <Z0onJRnxQ8ZaWeov@casper.infradead.org>
Date: Fri, 29 Nov 2024 20:42:13 +0000
From: Matthew Wilcox <willy@...radead.org>
To: David Hildenbrand <david@...hat.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Namhyung Kim <namhyung@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Jiri Olsa <jolsa@...nel.org>, Ian Rogers <irogers@...gle.com>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Kan Liang <kan.liang@...ux.intel.com>,
	linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [PATCH] perf: map pages in advance

On Fri, Nov 29, 2024 at 03:48:33PM +0100, David Hildenbrand wrote:
> Too long, but as some of these TODOs stand in the memdesc way, fortunately
> other people might be able to give a helping hand at some point ;)

;-)

> I'll play with using a page type for some of these "simple" cases and see
> how hard it will get.

I've deliberately made pagetype incompatible with setting a mapcount ...
hugetlb being the exception because we only use entire_mapcount.

Anyway, I agree we need something better than what we have here.
It needs to be simple for a device driver to allocate memory and
map it into userspace.  I'm willing to allow perf's ringbuffer to be
a bit harder than most because it's trying to do the weird thing of
writable-first-page-rest-read-only.