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At memory hot-remove time we can retrieve an LMB's nid from its
corresponding memory_block. There is no need to store the nid
in multiple locations.
Note that lmb_to_memblock() uses find_memory_block() to get the
corresponding memory_block. As find_memory_block() runs in sub-linear
time this approach is negligibly slower than what we do at present.
In exchange for this lookup at hot-remove time we no longer need to
call memory_add_physaddr_to_nid() during drmem_init() for each LMB.
On powerpc, memory_add_physaddr_to_nid() is a linear search, so this
spares us an O(n^2) initialization during boot.
On systems with many LMBs that initialization overhead is palpable and
disruptive. For example, on a box with 249854 LMBs we're seeing
drmem_init() take upwards of 30 seconds to complete:
[ 53.721639] drmem: initializing drmem v2
[ 80.604346] watchdog: BUG: soft lockup - CPU#65 stuck for 23s! [swapper/0:1]
[ 80.604377] Modules linked in:
[ 80.604389] CPU: 65 PID: 1 Comm: swapper/0 Not tainted 5.6.0-rc2+ #4
[ 80.604397] NIP: c0000000000a4980 LR: c0000000000a4940 CTR: 0000000000000000
[ 80.604407] REGS: c0002dbff8493830 TRAP: 0901 Not tainted (5.6.0-rc2+)
[ 80.604412] MSR: 8000000002009033 <SF,VEC,EE,ME,IR,DR,RI,LE> CR: 44000248 XER: 0000000d
[ 80.604431] CFAR: c0000000000a4a38 IRQMASK: 0
[ 80.604431] GPR00: c0000000000a4940 c0002dbff8493ac0 c000000001904400 c0003cfffffede30
[ 80.604431] GPR04: 0000000000000000 c000000000f4095a 000000000000002f 0000000010000000
[ 80.604431] GPR08: c0000bf7ecdb7fb8 c0000bf7ecc2d3c8 0000000000000008 c00c0002fdfb2001
[ 80.604431] GPR12: 0000000000000000 c00000001e8ec200
[ 80.604477] NIP [c0000000000a4980] hot_add_scn_to_nid+0xa0/0x3e0
[ 80.604486] LR [c0000000000a4940] hot_add_scn_to_nid+0x60/0x3e0
[ 80.604492] Call Trace:
[ 80.604498] [c0002dbff8493ac0] [c0000000000a4940] hot_add_scn_to_nid+0x60/0x3e0 (unreliable)
[ 80.604509] [c0002dbff8493b20] [c000000000087c10] memory_add_physaddr_to_nid+0x20/0x60
[ 80.604521] [c0002dbff8493b40] [c0000000010d4880] drmem_init+0x25c/0x2f0
[ 80.604530] [c0002dbff8493c10] [c000000000010154] do_one_initcall+0x64/0x2c0
[ 80.604540] [c0002dbff8493ce0] [c0000000010c4aa0] kernel_init_freeable+0x2d8/0x3a0
[ 80.604550] [c0002dbff8493db0] [c000000000010824] kernel_init+0x2c/0x148
[ 80.604560] [c0002dbff8493e20] [c00000000000b648] ret_from_kernel_thread+0x5c/0x74
[ 80.604567] Instruction dump:
[ 80.604574] 392918e8 e9490000 e90a000a e92a0000 80ea000c 1d080018 3908ffe8 7d094214
[ 80.604586] 7fa94040 419d00dc e9490010 714a0088 <2faa0008> 409e00ac e9490000 7fbe5040
[ 89.047390] drmem: 249854 LMB(s)
With a patched kernel on the same machine we're no longer seeing the
soft lockup. drmem_init() now completes in negligible time, even when
the LMB count is large.
Fixes: b2d3b5ee66 ("powerpc/pseries: Track LMB nid instead of using device tree")
Signed-off-by: Scott Cheloha <cheloha@linux.ibm.com>
Reviewed-by: Nathan Lynch <nathanl@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200811015115.63677-1-cheloha@linux.ibm.com
e5e179aa3a