Messages in this thread | | | Date | Mon, 16 Nov 2015 15:22:54 -0500 | From | Johannes Weiner <> | Subject | Re: [PATCH] mm: vmpressure: fix scan window after SWAP_CLUSTER_MAX increase |
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Dear Hugh,
[ sorry, I just noticed this email now ]
On Wed, Oct 21, 2015 at 01:05:53PM -0700, Hugh Dickins wrote: > On Wed, 21 Oct 2015, Johannes Weiner wrote: > > On Mon, Oct 19, 2015 at 02:13:01PM -0400, Johannes Weiner wrote: > > > mm-increase-swap_cluster_max-to-batch-tlb-flushes.patch changed > > > SWAP_CLUSTER_MAX from 32 pages to 256 pages, inadvertantly switching > > > the scan window for vmpressure detection from 2MB to 16MB. Revert. > > > > > > Signed-off-by: Johannes Weiner <hannes@cmpxchg.org> > > > --- > > > mm/vmpressure.c | 2 +- > > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > > > diff --git a/mm/vmpressure.c b/mm/vmpressure.c > > > index c5afd57..74f206b 100644 > > > --- a/mm/vmpressure.c > > > +++ b/mm/vmpressure.c > > > @@ -38,7 +38,7 @@ > > > * TODO: Make the window size depend on machine size, as we do for vmstat > > > * thresholds. Currently we set it to 512 pages (2MB for 4KB pages). > > > */ > > > -static const unsigned long vmpressure_win = SWAP_CLUSTER_MAX * 16; > > > +static const unsigned long vmpressure_win = SWAP_CLUSTER_MAX; > > > > Argh, Mel's patch sets SWAP_CLUSTER_MAX to 256, so this should be > > SWAP_CLUSTER_MAX * 2 to retain the 512 pages scan window. > > > > Andrew could you please update this fix in-place? Otherwise I'll > > resend a corrected version. > > > > Thanks, and sorry about that. > > I don't understand why "SWAP_CLUSTER_MAX * 2" is thought better than "512". > Retaining a level of obscurity, that just bit us twice, is a good thing?
I'm not sure it is. But it doesn't seem entirely wrong to link it to the reclaim scan window, either--at least be a multiple of it so that the vmpressure reporting happens cleanly at the end of a scan cycle?
I don't mind changing it to 512, but it doesn't feel like an obvious improvement, either.
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