On Mon, May 16, 2011 at 12:27 AM, Wu Fengguang <fengguang.wu@xxxxxxxxx> wrote: > On Sun, May 15, 2011 at 09:37:58AM +0800, Minchan Kim wrote: >> On Sun, May 15, 2011 at 2:43 AM, Andi Kleen <andi@xxxxxxxxxxxxxx> wrote: >> > Copying back linux-mm. >> > >> >> Recently, we added following patch. >> >> https://lkml.org/lkml/2011/4/26/129 >> >> If it's a culprit, the patch should solve the problem. >> > >> > It would be probably better to not do the allocations at all under >> > memory pressure. ÂEven if the RA allocation doesn't go into reclaim >> >> Fair enough. >> I think we can do it easily now. >> If page_cache_alloc_readahead(ie, GFP_NORETRY) is fail, we can adjust >> RA window size or turn off a while. The point is that we can use the >> fail of __do_page_cache_readahead as sign of memory pressure. >> Wu, What do you think? > > No, disabling readahead can hardly help. I don't mean we have to disable RA. As I said, the point is that we can use __GFP_NORETRY alloc fail as _sign_ of memory pressure. > > The sequential readahead memory consumption can be estimated by > > Â Â Â Â Â Â Â Â2 * (number of concurrent read streams) * (readahead window size) > > And you can double that when there are two level of readaheads. > > Since there are hardly any concurrent read streams in Andy's case, > the readahead memory consumption will be ignorable. > > Typically readahead thrashing will happen long before excessive > GFP_NORETRY failures, so the reasonable solutions are to If it is, RA thrashing could be better sign than failure of __GFP_NORETRY. If we can do it easily, I don't object it. :) > > - shrink readahead window on readahead thrashing > Â(current readahead heuristic can somehow do this, and I have patches > Âto further improve it) Good to hear. :) I don't want RA steals high order page in memory pressure. My patch and shrinking RA window helps this case. -- Kind regards, Minchan Kim -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx 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