On Mon, Apr 18, 2011 at 10:32:51PM +1000, NeilBrown wrote: > On Thu, 14 Apr 2011 11:41:38 +0100 Mel Gorman <mgorman@xxxxxxx> wrote: > > > If swap is backed by network storage such as NBD, there is a risk that a > > large number of reclaimers can hang the system by consuming all > > PF_MEMALLOC reserves. To avoid these hangs, the administrator must tune > > min_free_kbytes in advance. This patch will throttle direct reclaimers > > if half the PF_MEMALLOC reserves are in use as the system is at risk of > > hanging. A message will be displayed so the administrator knows that > > min_free_kbytes should be tuned to a higher value to avoid the > > throttling in the future. > > > > (I knew there was something else). > > I understand that there are suggestions that direct reclaim should always be > serialised as this reduces lock contention and improve data patterns (or > something like that). > AFAIK, this suggestion never got much beyond the "hand-waving" stage of development. It tended to trip up on the fact that such a feature could also throttle processes on machines with plenty of free clean unmapped pagecache which would be undesirable. > Would that make this patch redundant? Depends on how it was being serialised but .... > Or does this provide some extra > guarantee that the other proposal would not? > This patch could be extended to serialise direct reclaims in situations other than PFMEMALLOC is low if someone demonstrated the benefit. -- Mel Gorman SUSE Labs -- 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=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>