On Tue, 05 May 2015 21:21:19 -0400 Waiman Long <waiman.long@xxxxxx> wrote: > On 05/05/2015 04:02 PM, Andrew Morton wrote: > > On Tue, 5 May 2015 11:45:14 +0100 Mel Gorman<mgorman@xxxxxxx> wrote: > > > >> On Mon, May 04, 2015 at 02:30:46PM -0700, Andrew Morton wrote: > >>>> Before the patch, the boot time from elilo prompt to ssh login was 694s. > >>>> After the patch, the boot up time was 346s, a saving of 348s (about 50%). > >>> Having to guesstimate the amount of memory which is needed for a > >>> successful boot will be painful. Any number we choose will be wrong > >>> 99% of the time. > >>> > >>> If the kswapd threads have started, all we need to do is to wait: take > >>> a little nap in the allocator's page==NULL slowpath. > >>> > >>> I'm not seeing any reason why we can't start kswapd much earlier - > >>> right at the start of do_basic_setup()? > >> It doesn't even have to be kswapd, it just should be a thread pinned to > >> a done. The difficulty is that dealing with the system hashes means the > >> initialisation has to happen before vfs_caches_init_early() when there is > >> no scheduler. > > I bet we can run vfs_caches_init_early() after sched_init(). Might > > need a few little fixups. > > > >> Those allocations could be delayed further but then there is > >> the possibility that the allocations would not be contiguous and they'd > >> have to rely on CMA to make the attempt. That potentially alters the > >> performance of the large system hashes at run time. > > hm, why. If the kswapd threads are running and busily creating free > > pages then alloc_pages(order=10) can detect this situation and stall > > for a while, waiting for kswapd to create an order-10 page. > > > > Alternatively, the page allocator can go off and synchronously > > initialize some pageframes itself. Keep doing that until the > > allocation attempt succeeds. > > > > Such an approach is much more robust than trying to predict how much > > memory will be needed. > > > > Most of those hash tables are allocated before smp_boot. In UP mode, you > can't have another thread initializing memory. So we really need to > preallocate enough for those tables. (copy-paste) : Alternatively, the page allocator can go off and synchronously : initialize some pageframes itself. Keep doing that until the : allocation attempt succeeds. IOW, the caller of alloc_pages() goes off and does the work which kswapd would have done later on. -- 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/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>