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@xxxxxxxxxx>
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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