Messages in this thread | | | Date | Tue, 05 May 2015 21:21:19 -0400 | From | Waiman Long <> | Subject | Re: [PATCH 0/13] Parallel struct page initialisation v4 |
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On 05/05/2015 04:02 PM, Andrew Morton wrote: > On Tue, 5 May 2015 11:45:14 +0100 Mel Gorman<mgorman@suse.de> 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.
Cheers, Longman
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