From: Bharata B Rao <bharata@linux•ibm.com>
To: linuxppc-dev@lists•ozlabs.org
Cc: leonardo@linux•ibm.com, aneesh.kumar@linux•vnet.ibm.com,
npiggin@gmail•com, Bharata B Rao <bharata@linux•ibm.com>
Subject: [RFC PATCH v0 2/5] powerpc/mm/radix: Create separate mappings for hot-plugged memory
Date: Mon, 6 Apr 2020 09:19:22 +0530 [thread overview]
Message-ID: <20200406034925.22586-3-bharata@linux.ibm.com> (raw)
In-Reply-To: <20200406034925.22586-1-bharata@linux.ibm.com>
Memory that gets hot-plugged _during_ boot (and not the memory
that gets plugged in after boot), is mapped with 1G mappings
and will undergo splitting when it is unplugged. The splitting
code has a few issues:
1. Recursive locking
--------------------
Memory unplug path takes cpu_hotplug_lock and calls stop_machine()
for splitting the mappings. However stop_machine() takes
cpu_hotplug_lock again causing deadlock.
2. BUG: sleeping function called from in_atomic() context
---------------------------------------------------------
Memory unplug path (remove_pagetable) takes init_mm.page_table_lock
spinlock and later calls stop_machine() which does wait_for_completion()
3. Bad unlock unbalance
-----------------------
Memory unplug path takes init_mm.page_table_lock spinlock and calls
stop_machine(). The stop_machine thread function runs in a different
thread context (migration thread) which tries to release and reaquire
ptl. Releasing ptl from a different thread than which acquired it
causes bad unlock unbalance.
These problems can be avoided if we avoid mapping hot-plugged memory
with 1G mapping, thereby removing the need for splitting them during
unplug. During radix init, identify(*) the hot-plugged memory region
and create separate mappings for each LMB so that they don't get mapped
with 1G mappings.
To create separate mappings for every LMB in the hot-plugged
region, we need lmb-size. I am currently using memory_block_size_bytes()
API to get the lmb-size. Since this is early init time code, the
machine type isn't probed yet and hence memory_block_size_bytes()
would return the default LMB size as 16MB. Hence we end up creating
separate mappings at much lower granularity than what we can ideally
do for pseries machine.
(*) Identifying and differentiating hot-plugged memory from the
boot time memory is now possible with PAPR extension to LMB flags.
(Ref: https://lore.kernel.org/linuxppc-dev/f55a7b65a43cc9dc7b22385cf9960f8b11d5ce2e.camel@linux.ibm.com/T/#t)
Signed-off-by: Bharata B Rao <bharata@linux•ibm.com>
---
arch/powerpc/mm/book3s64/radix_pgtable.c | 15 ++++++++++++---
1 file changed, 12 insertions(+), 3 deletions(-)
diff --git a/arch/powerpc/mm/book3s64/radix_pgtable.c b/arch/powerpc/mm/book3s64/radix_pgtable.c
index dd1bea45325c..4a4fb30f6c3d 100644
--- a/arch/powerpc/mm/book3s64/radix_pgtable.c
+++ b/arch/powerpc/mm/book3s64/radix_pgtable.c
@@ -16,6 +16,7 @@
#include <linux/hugetlb.h>
#include <linux/string_helpers.h>
#include <linux/stop_machine.h>
+#include <linux/memory.h>
#include <asm/pgtable.h>
#include <asm/pgalloc.h>
@@ -313,6 +314,8 @@ static void __init radix_init_pgtable(void)
{
unsigned long rts_field;
struct memblock_region *reg;
+ phys_addr_t addr;
+ u64 lmb_size = memory_block_size_bytes();
/* We don't support slb for radix */
mmu_slb_size = 0;
@@ -331,9 +334,15 @@ static void __init radix_init_pgtable(void)
continue;
}
- WARN_ON(create_physical_mapping(reg->base,
- reg->base + reg->size,
- -1));
+ if (memblock_is_hotpluggable(reg)) {
+ for (addr = reg->base; addr < (reg->base + reg->size);
+ addr += lmb_size)
+ WARN_ON(create_physical_mapping(addr,
+ addr + lmb_size, -1));
+ } else
+ WARN_ON(create_physical_mapping(reg->base,
+ reg->base + reg->size,
+ -1));
}
/* Find out how many PID bits are supported */
--
2.21.0
next prev parent reply other threads:[~2020-04-06 3:55 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-06 3:49 [RFC PATCH v0 0/5] powerpc/mm/radix: Memory unplug fixes Bharata B Rao
2020-04-06 3:49 ` [RFC PATCH v0 1/5] powerpc/pseries/hotplug-memory: Set DRCONF_MEM_HOTREMOVABLE for hot-plugged mem Bharata B Rao
2020-04-06 3:49 ` Bharata B Rao [this message]
2020-06-22 12:46 ` [RFC PATCH v0 2/5] powerpc/mm/radix: Create separate mappings for hot-plugged memory Aneesh Kumar K.V
2020-04-06 3:49 ` [RFC PATCH v0 3/5] powerpc/mm/radix: Fix PTE/PMD fragment count for early page table mappings Bharata B Rao
2020-06-22 12:53 ` Aneesh Kumar K.V
2020-06-22 13:22 ` Aneesh Kumar K.V
2020-04-06 3:49 ` [RFC PATCH v0 4/5] powerpc/mm/radix: Free PUD table when freeing pagetable Bharata B Rao
2020-06-22 13:07 ` Aneesh Kumar K.V
2020-04-06 3:49 ` [RFC PATCH v0 5/5] powerpc/mm/radix: Remove split_kernel_mapping() Bharata B Rao
2020-06-22 13:07 ` Aneesh Kumar K.V
2020-04-09 4:31 ` [RFC PATCH v0 0/5] powerpc/mm/radix: Memory unplug fixes Bharata B Rao
2020-05-20 4:34 ` Bharata B Rao
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20200406034925.22586-3-bharata@linux.ibm.com \
--to=bharata@linux$(echo .)ibm.com \
--cc=aneesh.kumar@linux$(echo .)vnet.ibm.com \
--cc=leonardo@linux$(echo .)ibm.com \
--cc=linuxppc-dev@lists$(echo .)ozlabs.org \
--cc=npiggin@gmail$(echo .)com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox