On Tuesday 06 October 2015 03:40 AM, Andrew Morton wrote: > On Sat, 3 Oct 2015 18:25:13 +0530 Vineet Gupta <Vineet.Gupta1@xxxxxxxxxxxx> wrote: > >> Hi, >> >> I noticed increased boot time when enabling highmem for ARC. Turns out that >> freeing highmem pages into buddy allocator is done page at a time, while it is >> batched for low mem pages. Below is call flow. >> >> I'm thinking of writing free_highmem_pages() which takes start and end pfn and >> want to solicit some ideas whether to write it from scratch or preferably call >> existing __free_pages_memory() to reuse the logic to convert a pfn range into >> {pfn, order} tuples. >> >> For latter however there are semantical differences as you can see below which I'm >> not sure of: >> -highmem page->count is set to 1, while 0 for low mem > That would be weird. > > Look more closely at __free_pages_boot_core() - it uses > set_page_refcounted() to set the page's refcount to 1. Those > set_page_count() calls look superfluous to me. If you closer still, set_page_refcounted() is called outside the loop for the first page only. For all pages, loop iterator sets them to 1. Turns out there's more fun here.... I ran this under a debugger and much earlier in boot process, there's existing setting of page count to 1 for *all* pages of *all* zones (include highmem pages). See call flow below. free_area_init_node free_area_init_core loops thru all zones memmap_init_zone loops thru all pages of zones __init_single_page This means the subsequent setting of page count to 0 (or 1 for the special first page) is superfluous - actually buggy at best. I will send a patch to fix that. I hope I don't break some obscure init path which doesn't hit the above init. > >> -atomic clearing of page reserved flag vs. non atomic > I doubt if the atomic is needed - who else can be looking at this page > at this time? I'll send another one to separately fix that as well. Seems like boot mem setup is a relatively neglect part of kernel. -Vineet -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html