[PATCH 5.9 412/757] pseries/drmem: dont cache node id in drmem_lmb struct

Greg Kroah-Hartman
2020-10-27T15:56:50Z

From: Scott Cheloha <cheloha@linux.ibm.com>

[ Upstream commit e5e179aa3a39c818db8fbc2dce8d2cd24adaf657 ]

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: b2d3b5ee66f2 ("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
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/powerpc/include/asm/drmem.h | 21 ----------------
arch/powerpc/mm/drmem.c | 6 +----
.../platforms/pseries/hotplug-memory.c | 24 ++++++++++++-------
3 files changed, 17 insertions(+), 34 deletions(-)

diff --git a/arch/powerpc/include/asm/drmem.h b/arch/powerpc/include/asm/drmem.h
index 6fb928605ed13..030a19d922132 100644
--- a/arch/powerpc/include/asm/drmem.h
+++ b/arch/powerpc/include/asm/drmem.h
@@ -15,9 +15,6 @@ struct drmem_lmb {
u32 drc_index;
u32 aa_index;
u32 flags;
-#ifdef CONFIG_MEMORY_HOTPLUG
- int nid;
-#endif
};

struct drmem_lmb_info {
@@ -121,22 +118,4 @@ static inline void invalidate_lmb_associativity_index(struct drmem_lmb *lmb)
lmb->aa_index = 0xffffffff;
}

-#ifdef CONFIG_MEMORY_HOTPLUG
-static inline void lmb_set_nid(struct drmem_lmb *lmb)
-{
- lmb->nid = memory_add_physaddr_to_nid(lmb->base_addr);
-}
-static inline void lmb_clear_nid(struct drmem_lmb *lmb)
-{
- lmb->nid = -1;
-}
-#else
-static inline void lmb_set_nid(struct drmem_lmb *lmb)
-{
-}
-static inline void lmb_clear_nid(struct drmem_lmb *lmb)
-{
-}
-#endif
-
#endif /* _ASM_POWERPC_LMB_H */
diff --git a/arch/powerpc/mm/drmem.c b/arch/powerpc/mm/drmem.c
index b2eeea39684ca..9af3832c9d8dc 100644
--- a/arch/powerpc/mm/drmem.c
+++ b/arch/powerpc/mm/drmem.c
@@ -389,10 +389,8 @@ static void __init init_drmem_v1_lmbs(const __be32 *prop)
if (!drmem_info->lmbs)
return;

- for_each_drmem_lmb(lmb) {
+ for_each_drmem_lmb(lmb)
read_drconf_v1_cell(lmb, &prop);
- lmb_set_nid(lmb);
- }
}

static void __init init_drmem_v2_lmbs(const __be32 *prop)
@@ -437,8 +435,6 @@ static void __init init_drmem_v2_lmbs(const __be32 *prop)

lmb->aa_index = dr_cell.aa_index;
lmb->flags = dr_cell.flags;
-
- lmb_set_nid(lmb);
}
}
}
diff --git a/arch/powerpc/platforms/pseries/hotplug-memory.c b/arch/powerpc/platforms/pseries/hotplug-memory.c
index 5d545b78111f9..0ea976d1cac47 100644
--- a/arch/powerpc/platforms/pseries/hotplug-memory.c
+++ b/arch/powerpc/platforms/pseries/hotplug-memory.c
@@ -354,25 +354,32 @@ static int dlpar_add_lmb(struct drmem_lmb *);

static int dlpar_remove_lmb(struct drmem_lmb *lmb)
{
+ struct memory_block *mem_block;
unsigned long block_sz;
int rc;

if (!lmb_is_removable(lmb))
return -EINVAL;

+ mem_block = lmb_to_memblock(lmb);
+ if (mem_block == NULL)
+ return -EINVAL;
+
rc = dlpar_offline_lmb(lmb);
- if (rc)
+ if (rc) {
+ put_device(&mem_block->dev);
return rc;
+ }

block_sz = pseries_memory_block_size();

- __remove_memory(lmb->nid, lmb->base_addr, block_sz);
+ __remove_memory(mem_block->nid, lmb->base_addr, block_sz);
+ put_device(&mem_block->dev);

/* Update memory regions for memory remove */
memblock_remove(lmb->base_addr, block_sz);

invalidate_lmb_associativity_index(lmb);
- lmb_clear_nid(lmb);
lmb->flags &= ~DRCONF_MEM_ASSIGNED;

return 0;
@@ -591,7 +598,7 @@ static int dlpar_memory_remove_by_ic(u32 lmbs_to_remove, u32 drc_index)
static int dlpar_add_lmb(struct drmem_lmb *lmb)
{
unsigned long block_sz;
- int rc;
+ int nid, rc;

if (lmb->flags & DRCONF_MEM_ASSIGNED)
return -EINVAL;
@@ -602,11 +609,13 @@ static int dlpar_add_lmb(struct drmem_lmb *lmb)
return rc;
}

- lmb_set_nid(lmb);
block_sz = memory_block_size_bytes();

+ /* Find the node id for this address. */
+ nid = memory_add_physaddr_to_nid(lmb->base_addr);
+
/* Add the memory */
- rc = __add_memory(lmb->nid, lmb->base_addr, block_sz);
+ rc = __add_memory(nid, lmb->base_addr, block_sz);
if (rc) {
invalidate_lmb_associativity_index(lmb);
return rc;
@@ -614,9 +623,8 @@ static int dlpar_add_lmb(struct drmem_lmb *lmb)

rc = dlpar_online_lmb(lmb);
if (rc) {
- __remove_memory(lmb->nid, lmb->base_addr, block_sz);
+ __remove_memory(nid, lmb->base_addr, block_sz);
invalidate_lmb_associativity_index(lmb);
- lmb_clear_nid(lmb);
} else {
lmb->flags |= DRCONF_MEM_ASSIGNED;
}
--
2.25.1