Andrea Arcangeli <[EMAIL PROTECTED]> wrote: > > On Wed, Mar 16, 2005 at 04:04:35AM -0800, Andrew Morton wrote: > > > + if (!reclaim_state->reclaimed_slab && > > > + zone->pages_scanned >= (zone->nr_active + > > > + zone->nr_inactive) * 4) > > > zone->all_unreclaimable = 1; > > > > That might not change anything because we clear ->all_unreclaimable in > > free_page_bulk(). [..] > > Really? free_page_bulk is called inside shrink_slab, and so it's overwritten > later by all_unreclaimable. Otherwise how could all_unreclaimable be set > in the first place if a single page freed by shrink_slab would be enough > to clear it? > > shrink_slab > all_unreclaimable = 0 > zone->pages_scanned >= (zone->nr_active [..] > all_unreclaimable = 1 > > try_to_free_pages > all_unreclaimable == 1 > oom
Spose so. > I also considering changing shrink_slab to return a progress retval, but > then I noticed I could get away with a one liner fix ;). > > Your fix is better but it should be mostly equivalent in pratcie. I > liked the dontrylock not risking to go oom, the one liner couldn't > handle that ;). It has a problem. If ZONE_DMA is really, really oom, kswapd will sit there freeing up ZONE_NORMAL slab objects and not setting all_unreclaimable. We'll end up using tons of CPU and reclaiming lots of slab in response to a ZONE_DMA oom. I'm thinking that the most accurate way of fixing this and also avoiding the "we're fragmenting slab but not actually freeing pages yet" problem is - change task_struct->reclaim_state so that it has an array of booleans (one per zone) - in kmem_cache_free, work out what zone the object corresponds to and set the boolean in current->reclaim_state which corresponds to that zone. - in balance_pgdat(), inspect this zone's boolean to see if we're making any forward progress with slab freeing. Probably we can do the work in kmem_cache_free() at the place where we spill the slab magazine, to optimise things a bit. I haven't looked at it. But that has a problem too. Some other task might be freeing objects into the relevant zone instead of this one. So maybe a better approach would be to add a "someone freed something" counter to the zone structure. That would be incremented whenever anyone frees a page for a slab object. Then in balance_pdgat we take a look at that before and after performing the LRU and slab scans. If it incremented, dont' set all_unreclaimable. And still keep the free_pages_bulk code there as the code which takes us _out_ of the all_unreclaimable state. It's tricky. - 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/
