linux-kernel - Re: [PATCH v2] perf: map pages in advance

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Message-ID: <Z0nl4B_71PP-yf4m@casper.infradead.org>
Date: Fri, 29 Nov 2024 16:03:44 +0000
From: Matthew Wilcox <willy@...radead.org>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Cc: 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, David Hildenbrand <david@...hat.com>
Subject: Re: [PATCH v2] perf: map pages in advance

On Fri, Nov 29, 2024 at 03:31:34PM +0000, Lorenzo Stoakes wrote:
> While it is not ideal to use a VM_PFNMAP here, doing anything else will
> result in the page_mkwrite() hook need to be provided, which requires the
> same page->mapping hack this patch seeks to undo.

Or we could map the first page read-write to begin with ... ?
Or we could implement a page_mkwrite handler, but do the permissions
change in the driver and return VM_FAULT_NOPAGE.

I don't think we should do the second option in this driver, but
mentioning it because we're going to need to have A Talk about fb_defio.