question on page-migration code

[Ray Bryant <raybry@engr.sgi.com>]

Hirokazu (and Marcelo),

In testing my manual page migration code, I've run up against a situation
where the migrations are occasionally very slow.  They work ok, but they
can take minutes to migrate a few megabytes of memory.

Dropping into kdb shows that the migration code is waiting in msleep() in
migrate_page_common() due to an -EAGAIN return from page_migratable().
A little further digging shows that the specific return in page_migratable()
is the very last one there at the bottom of the routine.

I'm puzzled as to why the page is still busy in this case.  Previous code
in page_migratable() has unmapped the page, its not in PageWriteback()
because we would have taken a different return statement in that case.

According to /proc/meminfo, there are no pages in either SwapCache or
Dirty state, and the system has been sync'd before the migrate_pages()
call was issued.
-- 
Best Regards,
Ray
-----------------------------------------------
                   Ray Bryant
512-453-9679 (work)         512-507-7807 (cell)
raybry@sgi.com             raybry@austin.rr.com
The box said: "Requires Windows 98 or better",
            so I installed Linux.
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