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    SubjectRe: [PATCH -mm] remove __GFP_NO_KSWAPD
    On 07/24/2012 07:34 PM, Minchan Kim wrote:
    > Hi Rik,
    >
    > On Tue, Jul 24, 2012 at 11:12:22AM -0400, Rik van Riel wrote:
    >> When transparent huge pages were introduced, memory compaction and
    >> swap storms were an issue, and the kernel had to be careful to not
    >> make THP allocations cause pageout or compaction.
    >>
    >> Now that we have working compaction deferral, kswapd is smart enough
    >> to invoke compaction and the quadratic behaviour around isolate_free_pages
    >> has been fixed, it should be safe to remove __GFP_NO_KSWAPD.
    >
    > Could you point out specific patches you mentiond which makes kswapd/compaction
    > smart? It will make description very clear.

    That could be a list of 50+ patches, merged over the
    last two or so years.

    In other words, such a large amount of data that it
    is unlikely to clarify the discussion...

    >> Signed-off-by: Rik van Riel <riel@redhat.com>
    >
    > I support it because I had a concern about that flags which is likely to be
    > used by other subsystems without careful thinking when the flag was introduced.
    > It's proved by mtd_kmalloc_up_to which was merged with sneaking without catching
    > from mm guys's eyes. When I read comment of that function, it seems to be proper
    > usage but I don't like it because it requries users of mm to know mm internal
    > like kswapd. So it should be avoided if possible.
    >
    > Plus, it means you need to fix it with show_gfp_flags. :)

    Ohh, a place I forgot to grep!

    I'll send in an incremental patch right now.

    >> ---
    >> This has been running fine on my system for a while, but my system
    >> only has 12GB and moderate memory pressure. I propose we keep this
    >> in -mm and -next for a while, and merge it for 3.7 if nobody complains.
    >
    > Yes. it should be very careful.
    > I guess Mel and Andrea would have opinions and benchmark.

    It's not as much benchmarks that I am worried about,
    but somebody running something unexpected on their
    system.




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