[PATCH v2] pseries/drmem: don't cache node id in drmem_lmb struct
Laurent Dufour
ldufour at linux.vnet.ibm.com
Thu Jul 30 01:32:13 AEST 2020
Hi Scott,
Le 28/07/2020 à 18:53, Scott Cheloha a écrit :
> 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.
>
> Signed-off-by: Scott Cheloha <cheloha at linux.ibm.com>
> ---
> arch/powerpc/include/asm/drmem.h | 21 -------------------
> arch/powerpc/mm/drmem.c | 6 +-----
> .../platforms/pseries/hotplug-memory.c | 19 ++++++++++-------
> 3 files changed, 13 insertions(+), 33 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/drmem.h b/arch/powerpc/include/asm/drmem.h
> index 414d209f45bb..34e4e9b257f5 100644
> --- a/arch/powerpc/include/asm/drmem.h
> +++ b/arch/powerpc/include/asm/drmem.h
> @@ -13,9 +13,6 @@ struct drmem_lmb {
> u32 drc_index;
> u32 aa_index;
> u32 flags;
> -#ifdef CONFIG_MEMORY_HOTPLUG
> - int nid;
> -#endif
> };
>
> struct drmem_lmb_info {
> @@ -104,22 +101,4 @@ 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 59327cefbc6a..873fcfc7b875 100644
> --- a/arch/powerpc/mm/drmem.c
> +++ b/arch/powerpc/mm/drmem.c
> @@ -362,10 +362,8 @@ 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)
> @@ -410,8 +408,6 @@ 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 5ace2f9a277e..7bf66fdcf916 100644
> --- a/arch/powerpc/platforms/pseries/hotplug-memory.c
> +++ b/arch/powerpc/platforms/pseries/hotplug-memory.c
> @@ -356,25 +356,29 @@ 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;
> +
lmb_to_memblock is 'getting' the memblock's device, so you should call
put_device(mem_block->device) to reverse that operation.
Something like:
--- a/arch/powerpc/platforms/pseries/hotplug-memory.c
+++ b/arch/powerpc/platforms/pseries/hotplug-memory.c
@@ -367,7 +367,7 @@ static int dlpar_remove_lmb(struct drmem_lmb *lmb)
rc = dlpar_offline_lmb(lmb);
if (rc)
- return rc;
+ goto out;
block_sz = pseries_memory_block_size();
@@ -379,7 +379,9 @@ static int dlpar_remove_lmb(struct drmem_lmb *lmb)
invalidate_lmb_associativity_index(lmb);
lmb->flags &= ~DRCONF_MEM_ASSIGNED;
- return 0;
+out:
+ put_device(&mem_block->dev);
+ return rc;
}
static int dlpar_memory_remove_by_count(u32 lmbs_to_remove)
> rc = dlpar_offline_lmb(lmb);
> if (rc)
> 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);
>
> /* 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;
> @@ -631,7 +635,7 @@ 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;
> @@ -642,11 +646,13 @@ 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);
This function is calling hot_add_drconf_scn_to_nid() which is walking all the
LMBs linearly, so we may spend a lot of time here.
I think it be nice to take some breath in the caller's loop in
dlpar_memory_add_by_count() to avoid soft lockup to be raised there when adding
a large number of LMBs, isn't it?
Nathan sent a patch to add such a breath in for_each_drmem_lmb_in_range() may be
it would be nice to add one in dlpar_memory_add_by_count() through that patch.
> +
> /* 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;
> @@ -654,9 +660,8 @@ 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;
> }
>
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