Re: [patch 162/178] mm: page_alloc: dump migrate-failed pages

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On Fri, Apr 30, 2021 at 12:01 AM Andrew Morton
<akpm@xxxxxxxxxxxxxxxxxxxx> wrote:
>
> From: Minchan Kim <minchan@xxxxxxxxxx>
> Subject: mm: page_alloc: dump migrate-failed pages
>
> Currently, debugging CMA allocation failures is quite limited.  The most
> common source of these failures seems to be page migration which doesn't
> provide any useful information on the reason of the failure by itself.
> alloc_contig_range can report those failures as it holds a list of
> migrate-failed pages.
>
> The information logged by dump_page() has already proven helpful for
> debugging allocation issues, like identifying long-term pinnings on
> ZONE_MOVABLE or MIGRATE_CMA.
>
> Let's use the dynamic debugging infrastructure, such that we avoid
> flooding the logs and creating a lot of noise on frequent
> alloc_contig_range() calls.  This information is helpful for debugging
> only.
>
> There are two ifdefery conditions to support common dyndbg options:
>
> - CONFIG_DYNAMIC_DEBUG_CORE && DYNAMIC_DEBUG_MODULE
>   It aims for supporting the feature with only specific file with
>   adding ccflags.
>
> - CONFIG_DYNAMIC_DEBUG
>   It aims for supporting the feature with system wide globally.
>
> A simple example to enable the feature:
>
> Admin could enable the dump like this(by default, disabled)
>
>         echo "func alloc_contig_dump_pages +p" > control
>
> Admin could disable it.
>
>         echo "func alloc_contig_dump_pages =_" > control
>
> Detail goes Documentation/admin-guide/dynamic-debug-howto.rst
>
> A concern is utility functions in dump_page use inconsistent
> loglevels. In the future, we might want to make the loglevels
> used inside dump_page() consistent and eventually rework the way
> we log the information here. See [1].
>

FWIW, the  "format ^$prefix" specifier allows selection of "classes"
of pr_debugs
examples:
"^drm:kms:" etc
"^drm:" too, for example to set +fmlt across entire subsystem
"gvt:"
"^Lo", "^MID", "^HI"
"^1:", "^2:", "^3:"

all hierarchy / set-creation is applied by authors




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