On Thu, 23 Aug 2007, Andrea Arcangeli wrote: > On Tue, Aug 21, 2007 at 03:32:25PM -0700, Christoph Lameter wrote: > > 1. Like in the earlier patchset allow reentry to reclaim under > > PF_MEMALLOC if we are out of all memory. > > Can you simply tweak on the may_writepage flag only to achieve the > second pass? We're talking here about a totally non-performance case, > almost impossible to hit in practice unless you do real weird things, > and certainly very unlikely to happen. So I'm unsure what's all that > complexity just to make a regular pass on the lru looking for clean > pages, something may_writepage=0 already does. >
Yes that is what the PF_MEMALLOC patch that I posted before does. This discussion gets me more and more to thinking that the recursive reclaim on PF_MEMALLOC is all that is needed for emergency situations (to get out of the "tight spot"). See http://marc.info/?l=linux-kernel&m=118710219116624&w=2 > If the PF_MEMALLOC is found empty, I agree entering reclaim a second > time with may_writepage=0 sounds theoretically a good idea (in > practice it should never be necessary). printk must also be printed to > warn the user he was risking to deadlock for real and he has to > increase the min_free_kbytes. Ok. I can add a printk to that one. > That sounds a bit risky, there are latency considerations here to > make, GFP_ATOMIC will run with irq locally disabled and it may hang > for indefinite amount of time (O(N)). So irq latency may break and it > may be better to lose a packet once in a while than to hang > interrupts. If you want to do this you'd probably need to add a new > GFP_ATOMIC_RECLAIM or similar. Well we could do the same as for PF_MEMALLOC: print a warning and then reclaim nevertheless if we cannot fail (We already have a GFP_NOFAIL flag). It is better to generate a latency than the system failing altogether. However the GFP_ATOMIC reclaim patchset is a bit more invasive (http://marc.info/?l=linux-mm&m=118710584014150&w=2). Maybe this is too much churn for the rare need of such a reclaim. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
