From: Joerg Roedel <jroedel@xxxxxxx>
Subject: x86/mm: split vmalloc_sync_all()
Commit 3f8fd02b1bf1 ("mm/vmalloc: Sync unmappings in
__purge_vmap_area_lazy()") introduced a call to vmalloc_sync_all() in the
vunmap() code-path. While this change was necessary to maintain
correctness on x86-32-pae kernels, it also adds additional cycles for
architectures that don't need it.
Specifically on x86-64 with CONFIG_VMAP_STACK=y some people reported
severe performance regressions in micro-benchmarks because it now also
calls the x86-64 implementation of vmalloc_sync_all() on vunmap(). But
the vmalloc_sync_all() implementation on x86-64 is only needed for newly
created mappings.
To avoid the unnecessary work on x86-64 and to gain the performance back,
split up vmalloc_sync_all() into two functions:
* vmalloc_sync_mappings(), and
* vmalloc_sync_unmappings()
Most call-sites to vmalloc_sync_all() only care about new mappings being
synchronized. The only exception is the new call-site added in the above
mentioned commit.
Shile Zhang directed us to a report of an 80% regression in reaim
throughput.
Link: http://lkml.kernel.org/r/20191009124418.8286-1-joro@xxxxxxxxxx
Link: https://lists.01.org/hyperkitty/list/lkp@xxxxxxxxxxxx/thread/4D3JPPHBNOSPFK2KEPC6KGKS6J25AIDB/
Link: http://lkml.kernel.org/r/20191113095530.228959-1-shile.zhang@xxxxxxxxxxxxxxxxx
Fixes: 3f8fd02b1bf1 ("mm/vmalloc: Sync unmappings in __purge_vmap_area_lazy()")
Signed-off-by: Joerg Roedel <jroedel@xxxxxxx>
Reported-by: kernel test robot <oliver.sang@xxxxxxxxx>
Reported-by: Shile Zhang <shile.zhang@xxxxxxxxxxxxxxxxx>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx> [GHES]
Tested-by: Borislav Petkov <bp@xxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
arch/x86/mm/fault.c | 26 ++++++++++++++++++++++++--
drivers/acpi/apei/ghes.c | 2 +-
include/linux/vmalloc.h | 5 +++--
kernel/notifier.c | 2 +-
mm/nommu.c | 10 +++++++---
mm/vmalloc.c | 11 +++++++----
6 files changed, 43 insertions(+), 13 deletions(-)
--- a/arch/x86/mm/fault.c~x86-mm-split-vmalloc_sync_all
+++ a/arch/x86/mm/fault.c
@@ -190,7 +190,7 @@ static inline pmd_t *vmalloc_sync_one(pg
return pmd_k;
}
-void vmalloc_sync_all(void)
+static void vmalloc_sync(void)
{
unsigned long address;
@@ -217,6 +217,16 @@ void vmalloc_sync_all(void)
}
}
+void vmalloc_sync_mappings(void)
+{
+ vmalloc_sync();
+}
+
+void vmalloc_sync_unmappings(void)
+{
+ vmalloc_sync();
+}
+
/*
* 32-bit:
*
@@ -319,11 +329,23 @@ out:
#else /* CONFIG_X86_64: */
-void vmalloc_sync_all(void)
+void vmalloc_sync_mappings(void)
{
+ /*
+ * 64-bit mappings might allocate new p4d/pud pages
+ * that need to be propagated to all tasks' PGDs.
+ */
sync_global_pgds(VMALLOC_START & PGDIR_MASK, VMALLOC_END);
}
+void vmalloc_sync_unmappings(void)
+{
+ /*
+ * Unmappings never allocate or free p4d/pud pages.
+ * No work is required here.
+ */
+}
+
/*
* 64-bit:
*
--- a/drivers/acpi/apei/ghes.c~x86-mm-split-vmalloc_sync_all
+++ a/drivers/acpi/apei/ghes.c
@@ -171,7 +171,7 @@ int ghes_estatus_pool_init(int num_ghes)
* New allocation must be visible in all pgd before it can be found by
* an NMI allocating from the pool.
*/
- vmalloc_sync_all();
+ vmalloc_sync_mappings();
rc = gen_pool_add(ghes_estatus_pool, addr, PAGE_ALIGN(len), -1);
if (rc)
--- a/include/linux/vmalloc.h~x86-mm-split-vmalloc_sync_all
+++ a/include/linux/vmalloc.h
@@ -141,8 +141,9 @@ extern int remap_vmalloc_range_partial(s
extern int remap_vmalloc_range(struct vm_area_struct *vma, void *addr,
unsigned long pgoff);
-void vmalloc_sync_all(void);
-
+void vmalloc_sync_mappings(void);
+void vmalloc_sync_unmappings(void);
+
/*
* Lowlevel-APIs (not for driver use!)
*/
--- a/kernel/notifier.c~x86-mm-split-vmalloc_sync_all
+++ a/kernel/notifier.c
@@ -519,7 +519,7 @@ NOKPROBE_SYMBOL(notify_die);
int register_die_notifier(struct notifier_block *nb)
{
- vmalloc_sync_all();
+ vmalloc_sync_mappings();
return atomic_notifier_chain_register(&die_chain, nb);
}
EXPORT_SYMBOL_GPL(register_die_notifier);
--- a/mm/nommu.c~x86-mm-split-vmalloc_sync_all
+++ a/mm/nommu.c
@@ -370,10 +370,14 @@ void vm_unmap_aliases(void)
EXPORT_SYMBOL_GPL(vm_unmap_aliases);
/*
- * Implement a stub for vmalloc_sync_all() if the architecture chose not to
- * have one.
+ * Implement a stub for vmalloc_sync_[un]mapping() if the architecture
+ * chose not to have one.
*/
-void __weak vmalloc_sync_all(void)
+void __weak vmalloc_sync_mappings(void)
+{
+}
+
+void __weak vmalloc_sync_unmappings(void)
{
}
--- a/mm/vmalloc.c~x86-mm-split-vmalloc_sync_all
+++ a/mm/vmalloc.c
@@ -1295,7 +1295,7 @@ static bool __purge_vmap_area_lazy(unsig
* First make sure the mappings are removed from all page-tables
* before they are freed.
*/
- vmalloc_sync_all();
+ vmalloc_sync_unmappings();
/*
* TODO: to calculate a flush range without looping.
@@ -3128,16 +3128,19 @@ int remap_vmalloc_range(struct vm_area_s
EXPORT_SYMBOL(remap_vmalloc_range);
/*
- * Implement a stub for vmalloc_sync_all() if the architecture chose not to
- * have one.
+ * Implement stubs for vmalloc_sync_[un]mappings () if the architecture chose
+ * not to have one.
*
* The purpose of this function is to make sure the vmalloc area
* mappings are identical in all page-tables in the system.
*/
-void __weak vmalloc_sync_all(void)
+void __weak vmalloc_sync_mappings(void)
{
}
+void __weak vmalloc_sync_unmappings(void)
+{
+}
static int f(pte_t *pte, unsigned long addr, void *data)
{
_
