linux-kernel - Re: [PATCH V6 01/16] perf/core: Add PERF_SAMPLE_DATA_PAGE

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Message-ID: <20200810213524.GI3982@worktop.programming.kicks-ass.net>
Date:   Mon, 10 Aug 2020 23:35:24 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Kan Liang <kan.liang@...ux.intel.com>
Cc:     acme@...nel.org, mingo@...hat.com, linux-kernel@...r.kernel.org,
        mark.rutland@....com, alexander.shishkin@...ux.intel.com,
        jolsa@...hat.com, eranian@...gle.com, ak@...ux.intel.com,
        dave.hansen@...el.com, kirill.shutemov@...ux.intel.com
Subject: Re: [PATCH V6 01/16] perf/core: Add PERF_SAMPLE_DATA_PAGE_SIZE

On Mon, Aug 10, 2020 at 02:24:21PM -0700, Kan Liang wrote:
> Current perf can report both virtual addresses and physical addresses,
> but not the page size. Without the page size information of the utilized
> page, users cannot decide whether to promote/demote large pages to
> optimize memory usage.
> 
> Add a new sample type for the data page size.
> 
> Current perf already has a facility to collect data virtual addresses.
> A page walker is required to walk the pages tables and calculate the
> page size from a given virtual address.
> 
> On some platforms, e.g., X86, the page walker is invoked in an NMI
> handler. So the page walker must be IRQ-safe and low overhead. Besides,
> the page walker should work for both user and kernel virtual address.
> The existing generic page walker, e.g., walk_page_range_novma(), is a
> little bit complex and doesn't guarantee the IRQ-safe. The follow_page()
> is only for user-virtual address.

s/IRQ/NMI/g