On Mon, 16 Nov 2015, Johannes Weiner wrote: > Dear Hugh, > > [ sorry, I just noticed this email now ] No problem: as you can see, I'm very far from keeping up myself. > > 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@xxxxxxxxxxx> > > > > --- > > > > 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. Never mind: I thought it worth calling out at the time, but now that your change is in, I've no reason to make a fuss over it - if it ever bites us again, we can rework it then. Besides, when I wrote, I hadn't noticed the comment there about SWAP_CLUSTER_MAX, just out of sight before the context of your fix: that would have to be reworded, and I don't know what it should say. Oh, it's all still mmotm stuff, not in 4.4-rc. Well, even so, forget my interjection: we've all got bigger fish to fry. Hugh -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>