linux-kernel - Re: [PATCH V5] x86/mm: Tracking linear mapping split events

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Date:   Thu, 28 Jan 2021 15:04:44 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     Saravanan D <saravanand@...com>
Cc:     x86@...nel.org, dave.hansen@...ux.intel.com, luto@...nel.org,
        peterz@...radead.org, corbet@....net, linux-kernel@...r.kernel.org,
        kernel-team@...com, linux-doc@...r.kernel.org, linux-mm@...ck.org,
        songliubraving@...com
Subject: Re: [PATCH V5] x86/mm: Tracking linear mapping split events

On Thu, Jan 28, 2021 at 02:49:34AM -0800, Saravanan D wrote:
> One of the many lasting (as we don't coalesce back) sources for huge page
> splits is tracing as the granular page attribute/permission changes would
> force the kernel to split code segments mapped to huge pages to smaller
> ones thereby increasing the probability of TLB miss/reload even after
> tracing has been stopped.

You didn't answer my question.

Is this tracing of userspace programs causing splits, or is it kernel
tracing?  Also, we have lots of kinds of tracing these days; are you
referring to kprobes?  tracepoints?  ftrace?  Something else?