linux-kernel - Re: [PATCH] mm/debug: sync up latest migrate_reason to migrate_reason

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Date:   Sat, 18 Sep 2021 15:03:32 +0800
From:   Weizhao Ouyang <o451686892@...il.com>
To:     John Hubbard <jhubbard@...dia.com>,
        "Huang, Ying" <ying.huang@...el.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Pavel Tatashin <pasha.tatashin@...een.com>,
        Oscar Salvador <osalvador@...e.de>,
        Yang Shi <shy828301@...il.com>, Zi Yan <ziy@...dia.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/debug: sync up latest migrate_reason to
 migrate_reason_names

On 2021/9/18 08:30, John Hubbard wrote:
> On 9/17/21 02:48, Weizhao Ouyang wrote:
> ...
>>>>   const struct trace_print_flags pageflag_names[] = {
>>> Good catch!  Thanks!
>>>
>>> Reviewed-by: "Huang, Ying" <ying.huang@...el.com>
>>>
>>> It may be better to use BUILD_BUG_ON() to capture similar issue earlier?
>>
>> How about move migrate_reason_names into mm/page_owner.c and make it size uninitialized(get rid of MR_TYPES).
>> Then use BUILD_BUG_ON(ARRAY_SIZE(migrate_reason_names != MR_TYPES)) to check it?
>>
> A couple more thoughts:
>
> 1) From a naming and location point of view, migrate_reason_names[]
> really doesn't want to be located in page_owner.c.

Commit 7cd12b4abfd2 ("mm, page_owner: track and print last migrate reason")
imported migrate_reason_names for page owner in mm/debug.c, and it only used
by page_owner.c now, maybe it's not so sensitive or we can rename it.

> 2) There are actually three places to synchronize, not two. And in fact,
> sure enough, the MR_CONTIG_RANGE is already drifting out of synch: it
> has a string of "cma" in mm/debug.c, versus "contig_range" in
> include/trace/events/migrate.h.

Yes, "cma" is out of synch after commit 310253514bbf ("mm/migrate: rename
migration reason MR_CMA to MR_CONTIG_RANGE"). Update it to "contig_range" in
migrate_reason_names can fix up it.

> So...is it possible to use the macro and enums in
> include/trace/events/migrate.h, to define the connection between
> migrate_reason and a string, everywhere?

As for synchronization, tracepoint use TRACE_DEFINE_ENUM() macro to map enums.
In general, this kind of synch between subsystem and trace event subsystem is
mostly conscious. So it more likes that include/linux/migrate.h is connected to
include/trace/events/migrate.h and migrate_reason_names, the others hasn't
relationship except same reason string.

Anyway, I didn't find a simply way the build the "everywhere" relationship behind
the packaged TRACE_DEFINE_ENUM , what do you think.

Thanks,
Weizhao