Hi, so while optimizing away the _mapcount tail page refcounting for slab and hugetlbfs pages incremental with the fix for the hugetlbfs optimization I just sent, I also noticed another bug in the current code (already fixed by the patch). gup_fast is still increasing _mapcount for hugetlbfs, but it's not decreased in put_page. It's only noticeable if you do: echo 0 >/sys/kernel/mm/hugepages/hugepages-2048kB/nr_hugepages On current upstream I get: BUG: Bad page state in process bash pfn:59a01 page:ffffea000139b038 count:0 mapcount:10 mapping: (null) index:0x0 page flags: 0x1c00000000008000(tail) Modules linked in: CPU: 6 PID: 2018 Comm: bash Not tainted 3.12.0+ #25 Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011 0000000000000009 ffff880079cb5cc8 ffffffff81640e8b 0000000000000006 ffffea000139b038 ffff880079cb5ce8 ffffffff8115bb15 00000000000002c1 ffffea000139b038 ffff880079cb5d48 ffffffff8115bd83 ffff880079cb5de8 Call Trace: [<ffffffff81640e8b>] dump_stack+0x55/0x76 [<ffffffff8115bb15>] bad_page+0xd5/0x130 [<ffffffff8115bd83>] free_pages_prepare+0x213/0x280 [<ffffffff8115df16>] __free_pages+0x36/0x80 [<ffffffff8119b011>] update_and_free_page+0xc1/0xd0 [<ffffffff8119b512>] free_pool_huge_page+0xc2/0xe0 [<ffffffff8119b8cc>] set_max_huge_pages.part.58+0x14c/0x220 [<ffffffff81308a8c>] ? _kstrtoull+0x2c/0x90 [<ffffffff8119ba70>] nr_hugepages_store_common.isra.60+0xd0/0xf0 [<ffffffff8119bac3>] nr_hugepages_store+0x13/0x20 [<ffffffff812f763f>] kobj_attr_store+0xf/0x20 [<ffffffff812354e9>] sysfs_write_file+0x189/0x1e0 [<ffffffff811baff5>] vfs_write+0xc5/0x1f0 [<ffffffff811bb505>] SyS_write+0x55/0xb0 [<ffffffff81651712>] system_call_fastpath+0x16/0x1b So good thing I stopped the hugetlbfs optimization from going into stable. I'll send a v2 of this work as a patchset of 3 patches where the first is the same identical patch I already sent but incremental to upstream and it contains all the fixes needed including for the above problem. Patch 1/3 should be applied more urgently as it fixes all those various bugs. The 2/3 and 3/3 can be deferred. The patch 3/3 especially should be benchmarked in the usual 8GB/sec setup before being applied, unless it makes a real difference I wouldn't apply it because it tends to slowdown the THP case a bit and it complicates things a bit more. -- 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>