[PATCH/RFC v2 0/3] tlb: mmu_gather: use batched table free if possible

[PATCH/RFC v2 0/3] tlb: mmu_gather: use batched table free if possible

[Nikita Yushchenko]

In mmu_gather code, the final table free in __tlb_remove_table_free()
executes a loop, calling arch hook __tlb_remove_table() to free each table
individually.

Several architectures use free_page_and_swap_cache() as their
__tlb_remove_table() implementation. Calling that in loop results into
individual calls to put_page() for each page being freed.

This patchset refactors the code to issue a single release_pages() call
in this case. This is expected to have better performance, especially when
memcg accounting is enabled.

Nikita Yushchenko (3):
  tlb: mmu_gather: introduce CONFIG_MMU_GATHER_TABLE_FREE_COMMON
  mm/swap: introduce free_pages_and_swap_cache_nolru()
  tlb: mmu_gather: use batched table free if possible

 arch/Kconfig                 |  3 +++
 arch/arm/Kconfig             |  1 +
 arch/arm/include/asm/tlb.h   |  5 -----
 arch/arm64/Kconfig           |  1 +
 arch/arm64/include/asm/tlb.h |  5 -----
 arch/x86/Kconfig             |  1 +
 arch/x86/include/asm/tlb.h   | 14 --------------
 include/asm-generic/tlb.h    |  5 +++++
 include/linux/swap.h         |  5 ++++-
 mm/mmu_gather.c              | 25 ++++++++++++++++++++++---
 mm/swap_state.c              | 29 ++++++++++++++++++++++-------
 11 files changed, 59 insertions(+), 35 deletions(-)

-- 
2.30.2

[PATCH/RFC v2 1/3] tlb: mmu_gather: introduce CONFIG_MMU_GATHER_TABLE_FREE_COMMON

[Nikita Yushchenko]

For architectures that use free_page_and_swap_cache() as their
__tlb_remove_table(), place that common implementation into
mm/mmu_gather.c, ifdef'ed by CONFIG_MMU_GATHER_TABLE_FREE_COMMON.

Signed-off-by: Nikita Yushchenko <nikita.yushchenko@virtuozzo.com>
---
 arch/Kconfig                 |  3 +++
 arch/arm/Kconfig             |  1 +
 arch/arm/include/asm/tlb.h   |  5 -----
 arch/arm64/Kconfig           |  1 +
 arch/arm64/include/asm/tlb.h |  5 -----
 arch/x86/Kconfig             |  1 +
 arch/x86/include/asm/tlb.h   | 14 --------------
 include/asm-generic/tlb.h    |  5 +++++
 mm/mmu_gather.c              | 10 ++++++++++
 9 files changed, 21 insertions(+), 24 deletions(-)

diff --git a/arch/Kconfig b/arch/Kconfig
index d3c4ab249e9c..9eba553cd86f 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -415,6 +415,9 @@ config HAVE_ARCH_JUMP_LABEL_RELATIVE
 config MMU_GATHER_TABLE_FREE
 	bool
 
+config MMU_GATHER_TABLE_FREE_COMMON
+	bool
+
 config MMU_GATHER_RCU_TABLE_FREE
 	bool
 	select MMU_GATHER_TABLE_FREE
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index c2724d986fa0..cc272e1ad12c 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -110,6 +110,7 @@ config ARM
 	select HAVE_PERF_REGS
 	select HAVE_PERF_USER_STACK_DUMP
 	select MMU_GATHER_RCU_TABLE_FREE if SMP && ARM_LPAE
+	select MMU_GATHER_TABLE_FREE_COMMON
 	select HAVE_REGS_AND_STACK_ACCESS_API
 	select HAVE_RSEQ
 	select HAVE_STACKPROTECTOR
diff --git a/arch/arm/include/asm/tlb.h b/arch/arm/include/asm/tlb.h
index b8cbe03ad260..9d9b21649ca0 100644
--- a/arch/arm/include/asm/tlb.h
+++ b/arch/arm/include/asm/tlb.h
@@ -29,11 +29,6 @@
 #include <linux/swap.h>
 #include <asm/tlbflush.h>
 
-static inline void __tlb_remove_table(void *_table)
-{
-	free_page_and_swap_cache((struct page *)_table);
-}
-
 #include <asm-generic/tlb.h>
 
 static inline void
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index c4207cf9bb17..0f99f30d99f6 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -196,6 +196,7 @@ config ARM64
 	select HAVE_FUNCTION_ARG_ACCESS_API
 	select HAVE_FUTEX_CMPXCHG if FUTEX
 	select MMU_GATHER_RCU_TABLE_FREE
+	select MMU_GATHER_TABLE_FREE_COMMON
 	select HAVE_RSEQ
 	select HAVE_STACKPROTECTOR
 	select HAVE_SYSCALL_TRACEPOINTS
diff --git a/arch/arm64/include/asm/tlb.h b/arch/arm64/include/asm/tlb.h
index c995d1f4594f..401826260a5c 100644
--- a/arch/arm64/include/asm/tlb.h
+++ b/arch/arm64/include/asm/tlb.h
@@ -11,11 +11,6 @@
 #include <linux/pagemap.h>
 #include <linux/swap.h>
 
-static inline void __tlb_remove_table(void *_table)
-{
-	free_page_and_swap_cache((struct page *)_table);
-}
-
 #define tlb_flush tlb_flush
 static void tlb_flush(struct mmu_gather *tlb);
 
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 5c2ccb85f2ef..379d6832d3de 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -235,6 +235,7 @@ config X86
 	select HAVE_PERF_REGS
 	select HAVE_PERF_USER_STACK_DUMP
 	select MMU_GATHER_RCU_TABLE_FREE		if PARAVIRT
+	select MMU_GATHER_TABLE_FREE_COMMON
 	select HAVE_POSIX_CPU_TIMERS_TASK_WORK
 	select HAVE_REGS_AND_STACK_ACCESS_API
 	select HAVE_RELIABLE_STACKTRACE		if X86_64 && (UNWINDER_FRAME_POINTER || UNWINDER_ORC) && STACK_VALIDATION
diff --git a/arch/x86/include/asm/tlb.h b/arch/x86/include/asm/tlb.h
index 1bfe979bb9bc..96e3b4f922c9 100644
--- a/arch/x86/include/asm/tlb.h
+++ b/arch/x86/include/asm/tlb.h
@@ -23,18 +23,4 @@ static inline void tlb_flush(struct mmu_gather *tlb)
 	flush_tlb_mm_range(tlb->mm, start, end, stride_shift, tlb->freed_tables);
 }
 
-/*
- * While x86 architecture in general requires an IPI to perform TLB
- * shootdown, enablement code for several hypervisors overrides
- * .flush_tlb_others hook in pv_mmu_ops and implements it by issuing
- * a hypercall. To keep software pagetable walkers safe in this case we
- * switch to RCU based table free (MMU_GATHER_RCU_TABLE_FREE). See the comment
- * below 'ifdef CONFIG_MMU_GATHER_RCU_TABLE_FREE' in include/asm-generic/tlb.h
- * for more details.
- */
-static inline void __tlb_remove_table(void *table)
-{
-	free_page_and_swap_cache(table);
-}
-
 #endif /* _ASM_X86_TLB_H */
diff --git a/include/asm-generic/tlb.h b/include/asm-generic/tlb.h
index 2c68a545ffa7..877431da21cf 100644
--- a/include/asm-generic/tlb.h
+++ b/include/asm-generic/tlb.h
@@ -158,6 +158,11 @@
  *  Useful if your architecture doesn't use IPIs for remote TLB invalidates
  *  and therefore doesn't naturally serialize with software page-table walkers.
  *
+ *  MMU_GATHER_TABLE_FREE_COMMON
+ *
+ *  Provide default implementation of __tlb_remove_table() based on
+ *  free_page_and_swap_cache().
+ *
  *  MMU_GATHER_NO_RANGE
  *
  *  Use this if your architecture lacks an efficient flush_tlb_range().
diff --git a/mm/mmu_gather.c b/mm/mmu_gather.c
index 1b9837419bf9..eb2f30a92462 100644
--- a/mm/mmu_gather.c
+++ b/mm/mmu_gather.c
@@ -93,6 +93,13 @@ bool __tlb_remove_page_size(struct mmu_gather *tlb, struct page *page, int page_
 
 #ifdef CONFIG_MMU_GATHER_TABLE_FREE
 
+#ifdef CONFIG_MMU_GATHER_TABLE_FREE_COMMON
+static inline void __tlb_remove_table(void *table)
+{
+	free_page_and_swap_cache((struct page *)table);
+}
+#endif
+
 static void __tlb_remove_table_free(struct mmu_table_batch *batch)
 {
 	int i;
@@ -132,6 +139,9 @@ static void __tlb_remove_table_free(struct mmu_table_batch *batch)
  * pressure. To guarantee progress we fall back to single table freeing, see
  * the implementation of tlb_remove_table_one().
  *
+ * This is also used to keep software pagetable walkers safe when architecture
+ * natively uses IPIs for TLB flushes, but hypervisor enablement code replaced
+ * that by issuing a hypercall.
  */
 
 static void tlb_remove_table_smp_sync(void *arg)
-- 
2.30.2

Re: [PATCH/RFC v2 1/3] tlb: mmu_gather: introduce CONFIG_MMU_GATHER_TABLE_FREE_COMMON

[Peter Zijlstra]

On Sat, Dec 18, 2021 at 09:52:04PM +0300, Nikita Yushchenko wrote:
> For architectures that use free_page_and_swap_cache() as their
> __tlb_remove_table(), place that common implementation into
> mm/mmu_gather.c, ifdef'ed by CONFIG_MMU_GATHER_TABLE_FREE_COMMON.
> 
> Signed-off-by: Nikita Yushchenko <nikita.yushchenko@virtuozzo.com>
> ---
>  arch/Kconfig                 |  3 +++
>  arch/arm/Kconfig             |  1 +
>  arch/arm/include/asm/tlb.h   |  5 -----
>  arch/arm64/Kconfig           |  1 +
>  arch/arm64/include/asm/tlb.h |  5 -----
>  arch/x86/Kconfig             |  1 +
>  arch/x86/include/asm/tlb.h   | 14 --------------
>  include/asm-generic/tlb.h    |  5 +++++
>  mm/mmu_gather.c              | 10 ++++++++++
>  9 files changed, 21 insertions(+), 24 deletions(-)
> 
> diff --git a/arch/Kconfig b/arch/Kconfig
> index d3c4ab249e9c..9eba553cd86f 100644
> --- a/arch/Kconfig
> +++ b/arch/Kconfig
> @@ -415,6 +415,9 @@ config HAVE_ARCH_JUMP_LABEL_RELATIVE
>  config MMU_GATHER_TABLE_FREE
>  	bool
>  
> +config MMU_GATHER_TABLE_FREE_COMMON
> +	bool

I don't like that name... The point isn't that it's common, the point is
that the page-table's are backed by pages.

Re: [PATCH/RFC v2 1/3] tlb: mmu_gather: introduce CONFIG_MMU_GATHER_TABLE_FREE_COMMON

[Nikita Yushchenko]

>> +config MMU_GATHER_TABLE_FREE_COMMON
>> +	bool
> 
> I don't like that name... The point isn't that it's common, the point is
> that the page-table's are backed by pages.

What is a better name?

MMU_GATHER_TABLE_FREE_PAGES?

MMU_GATHER_TABLE_FREE_PAGES_BACKED?

Nikita

[PATCH/RFC v2 2/3] mm/swap: introduce free_pages_and_swap_cache_nolru()

[Nikita Yushchenko]

This is a variant of free_pages_and_swap_cache() that does not call
lru_add_drain(), for better performance in case when the passed pages
are guaranteed to not be in LRU.

Signed-off-by: Nikita Yushchenko <nikita.yushchenko@virtuozzo.com>
---
 include/linux/swap.h |  5 ++++-
 mm/swap_state.c      | 29 ++++++++++++++++++++++-------
 2 files changed, 26 insertions(+), 8 deletions(-)

diff --git a/include/linux/swap.h b/include/linux/swap.h
index d1ea44b31f19..86a1b0a61889 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -460,6 +460,7 @@ extern void clear_shadow_from_swap_cache(int type, unsigned long begin,
 extern void free_swap_cache(struct page *);
 extern void free_page_and_swap_cache(struct page *);
 extern void free_pages_and_swap_cache(struct page **, int);
+extern void free_pages_and_swap_cache_nolru(struct page **, int);
 extern struct page *lookup_swap_cache(swp_entry_t entry,
 				      struct vm_area_struct *vma,
 				      unsigned long addr);
@@ -565,7 +566,9 @@ static inline struct address_space *swap_address_space(swp_entry_t entry)
 #define free_page_and_swap_cache(page) \
 	put_page(page)
 #define free_pages_and_swap_cache(pages, nr) \
-	release_pages((pages), (nr));
+	release_pages((pages), (nr))
+#define free_pages_and_swap_cache_nolru(pages, nr) \
+	release_pages((pages), (nr))
 
 static inline void free_swap_cache(struct page *page)
 {
diff --git a/mm/swap_state.c b/mm/swap_state.c
index 8d4104242100..a5d9fd258f0a 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -307,17 +307,32 @@ void free_page_and_swap_cache(struct page *page)
 
 /*
  * Passed an array of pages, drop them all from swapcache and then release
- * them.  They are removed from the LRU and freed if this is their last use.
+ * them.  They are optionally removed from the LRU and freed if this is their
+ * last use.
  */
-void free_pages_and_swap_cache(struct page **pages, int nr)
+static void __free_pages_and_swap_cache(struct page **pages, int nr,
+		bool do_lru)
 {
-	struct page **pagep = pages;
 	int i;
 
-	lru_add_drain();
-	for (i = 0; i < nr; i++)
-		free_swap_cache(pagep[i]);
-	release_pages(pagep, nr);
+	if (do_lru)
+		lru_add_drain();
+	for (i = 0; i < nr; i++) {
+		if (!do_lru)
+			VM_WARN_ON_ONCE_PAGE(PageLRU(pages[i]), pages[i]);
+		free_swap_cache(pages[i]);
+	}
+	release_pages(pages, nr);
+}
+
+void free_pages_and_swap_cache(struct page **pages, int nr)
+{
+	__free_pages_and_swap_cache(pages, nr, true);
+}
+
+void free_pages_and_swap_cache_nolru(struct page **pages, int nr)
+{
+	__free_pages_and_swap_cache(pages, nr, false);
 }
 
 static inline bool swap_use_vma_readahead(void)
-- 
2.30.2

[PATCH/RFC v2 3/3] tlb: mmu_gather: use batched table free if possible

[Nikita Yushchenko]

In case when __tlb_remove_table() is implemented via
free_page_and_swap_cache(), use free_pages_and_swap_cache_nolru() for
batch table removal.

This enables use of single release_pages() call instead of a loop
calling put_page(). This shall have better performance, especially when
memcg accounting is enabled.

Signed-off-by: Nikita Yushchenko <nikita.yushchenko@virtuozzo.com>
---
 mm/mmu_gather.c | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/mm/mmu_gather.c b/mm/mmu_gather.c
index eb2f30a92462..2e75d396bbad 100644
--- a/mm/mmu_gather.c
+++ b/mm/mmu_gather.c
@@ -98,15 +98,24 @@ static inline void __tlb_remove_table(void *table)
 {
 	free_page_and_swap_cache((struct page *)table);
 }
-#endif
 
-static void __tlb_remove_table_free(struct mmu_table_batch *batch)
+static inline void __tlb_remove_tables(void **tables, int nr)
+{
+	free_pages_and_swap_cache_nolru((struct page **)tables, nr);
+}
+#else
+static inline void __tlb_remove_tables(void **tables, int nr)
 {
 	int i;
 
-	for (i = 0; i < batch->nr; i++)
-		__tlb_remove_table(batch->tables[i]);
+	for (i = 0; i < nr; i++)
+		__tlb_remove_table(tables[i]);
+}
+#endif
 
+static void __tlb_remove_table_free(struct mmu_table_batch *batch)
+{
+	__tlb_remove_tables(batch->tables, batch->nr);
 	free_page((unsigned long)batch);
 }
 
-- 
2.30.2