Re: [PATCH 3/4] mm: vmscan: Evaluate the watermarks against thecorrect classzone

[Minchan Kim]

On Tue, Jun 28, 2011 at 9:52 PM, Mel Gorman <mgorman@xxxxxxx> wrote:
> On Mon, Jun 27, 2011 at 03:53:04PM +0900, Minchan Kim wrote:
>> On Fri, Jun 24, 2011 at 11:44 PM, Mel Gorman <mgorman@xxxxxxx> wrote:
>> > When deciding if kswapd is sleeping prematurely, the classzone is
>> > taken into account but this is different to what balance_pgdat() and
>> > the allocator are doing. Specifically, the DMA zone will be checked
>> > based on the classzone used when waking kswapd which could be for a
>> > GFP_KERNEL or GFP_HIGHMEM request. The lowmem reserve limit kicks in,
>> > the watermark is not met and kswapd thinks its sleeping prematurely
>> > keeping kswapd awake in error.
>>
>>
>> I thought it was intentional when you submitted a patch firstly.
>
> It was, it also wasn't right.
>
>> "Kswapd makes sure zones include enough free pages(ie, include reserve
>> limit of above zones).
>> But you seem to see DMA zone can't meet above requirement forever in
>> some situation so that kswapd doesn't sleep.
>> Right?
>>
>
> Right.
>
>> >
>> > Reported-and-tested-by: PÃdraig Brady <P@xxxxxxxxxxxxxx>
>> > Signed-off-by: Mel Gorman <mgorman@xxxxxxx>
>> > ---
>> > Âmm/vmscan.c | Â Â2 +-
>> > Â1 files changed, 1 insertions(+), 1 deletions(-)
>> >
>> > diff --git a/mm/vmscan.c b/mm/vmscan.c
>> > index 9cebed1..a76b6cc2 100644
>> > --- a/mm/vmscan.c
>> > +++ b/mm/vmscan.c
>> > @@ -2341,7 +2341,7 @@ static bool sleeping_prematurely(pg_data_t *pgdat, int order, long remaining,
>> > Â Â Â Â Â Â Â Â}
>> >
>> > Â Â Â Â Â Â Â Âif (!zone_watermark_ok_safe(zone, order, high_wmark_pages(zone),
>> > - Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â classzone_idx, 0))
>> > + Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â i, 0))
>>
>> Isn't it Âbetter to use 0 instead of i?
>>
>
> I considered it but went with i to compromise between making sure zones
> included enough free pages without requiring that ZONE_DMA meet an
> almost impossible requirement when under continual memory pressure.

I see.
Thanks, Mel.

-- 
Kind regards,
Minchan Kim
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/