On Thu, Aug 11, 2011 at 02:18:54PM -0400, Rik van Riel wrote: > On 08/10/2011 06:47 AM, Mel Gorman wrote: > >It is preferable that no dirty pages are dispatched for cleaning from > >the page reclaim path. At normal priorities, this patch prevents kswapd > >writing pages. > > > >However, page reclaim does have a requirement that pages be freed > >in a particular zone. If it is failing to make sufficient progress > >(reclaiming< SWAP_CLUSTER_MAX at any priority priority), the priority > >is raised to scan more pages. A priority of DEF_PRIORITY - 3 is > >considered to be the point where kswapd is getting into trouble > >reclaiming pages. If this priority is reached, kswapd will dispatch > >pages for writing. > > > >Signed-off-by: Mel Gorman<mgorman@xxxxxxx> > >Reviewed-by: Minchan Kim<minchan.kim@xxxxxxxxx> > > My only worry with this patch is that maybe we'll burn too > much CPU time freeing pages from a zone. The throttling patch prevents too much CPU being used if pages under writeback are being encountered during scanning. That said, I shared your concern and recorded kswapd CPU usage over time. > However, chances > are we'll have freed pages from other zones when scanning > one zone multiple times (the page cache dirty limit is global, > the clean pages have to be _somewhere_). > > Since the bulk of the allocators are not too picky about > which zone they get their pages from, I suspect this patch > will be an overall improvement pretty much all the time. > This is roughly similar to my own reasoning. I uploaded all the kswapd CPU usage charts to http://www.csn.ul.ie/~mel/postings/riel-20110811 These are smoothened as the raw figures are barely readable. If you go through them, you'll see that kswapd CPU usage is sometimes higher but generally within 2-3%. > Acked-by: Rik van Riel <riel@xxxxxxxxxx> Thanks. -- Mel Gorman SUSE Labs -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>