The patch titled
Subject: x86: mm: free page table pages by RCU instead of semi RCU
has been added to the -mm mm-unstable branch. Its filename is
x86-mm-free-page-table-pages-by-rcu-instead-of-semi-rcu.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/x86-mm-free-page-table-pages-by-rcu-instead-of-semi-rcu.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>
Subject: x86: mm: free page table pages by RCU instead of semi RCU
Date: Wed, 4 Dec 2024 19:09:50 +0800
Now, if CONFIG_MMU_GATHER_RCU_TABLE_FREE is selected, the page table pages
will be freed by semi RCU, that is:
- batch table freeing: asynchronous free by RCU
- single table freeing: IPI + synchronous free
In this way, the page table can be lockless traversed by disabling IRQ in
paths such as fast GUP. But this is not enough to free the empty PTE page
table pages in paths other that munmap and exit_mmap path, because IPI
cannot be synchronized with rcu_read_lock() in pte_offset_map{_lock}().
In preparation for supporting empty PTE page table pages reclaimation, let
single table also be freed by RCU like batch table freeing. Then we can
also use pte_offset_map() etc to prevent PTE page from being freed.
Like pte_free_defer(), we can also safely use ptdesc->pt_rcu_head to free
the page table pages:
- The pt_rcu_head is unioned with pt_list and pmd_huge_pte.
- For pt_list, it is used to manage the PGD page in x86. Fortunately
tlb_remove_table() will not be used for free PGD pages, so it is safe
to use pt_rcu_head.
- For pmd_huge_pte, it is used for THPs, so it is safe.
After applying this patch, if CONFIG_PT_RECLAIM is enabled, the function
call of free_pte() is as follows:
free_pte
pte_free_tlb
__pte_free_tlb
___pte_free_tlb
paravirt_tlb_remove_table
tlb_remove_table [!CONFIG_PARAVIRT, Xen PV, Hyper-V, KVM]
[no-free-memory slowpath:]
tlb_table_invalidate
tlb_remove_table_one
__tlb_remove_table_one [frees via RCU]
[fastpath:]
tlb_table_flush
tlb_remove_table_free [frees via RCU]
native_tlb_remove_table [CONFIG_PARAVIRT on native]
tlb_remove_table [see above]
Link: https://lkml.kernel.org/r/0287d442a973150b0e1019cc406e6322d148277a.1733305182.git.zhengqi.arch@xxxxxxxxxxxxx
Signed-off-by: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Jann Horn <jannh@xxxxxxxxxx>
Cc: Lorenzo Stoakes <lorenzo.stoakes@xxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxx>
Cc: Muchun Song <muchun.song@xxxxxxxxx>
Cc: Peter Xu <peterx@xxxxxxxxxx>
Cc: Will Deacon <will@xxxxxxxxxx>
Cc: Zach O'Keefe <zokeefe@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
arch/x86/include/asm/tlb.h | 20 ++++++++++++++++++++
arch/x86/kernel/paravirt.c | 7 +++++++
arch/x86/mm/pgtable.c | 10 +++++++++-
include/linux/mm_types.h | 4 +++-
mm/mmu_gather.c | 9 ++++++++-
5 files changed, 47 insertions(+), 3 deletions(-)
--- a/arch/x86/include/asm/tlb.h~x86-mm-free-page-table-pages-by-rcu-instead-of-semi-rcu
+++ a/arch/x86/include/asm/tlb.h
@@ -34,8 +34,28 @@ static inline void __tlb_remove_table(vo
free_page_and_swap_cache(table);
}
+#ifdef CONFIG_PT_RECLAIM
+static inline void __tlb_remove_table_one_rcu(struct rcu_head *head)
+{
+ struct page *page;
+
+ page = container_of(head, struct page, rcu_head);
+ put_page(page);
+}
+
+static inline void __tlb_remove_table_one(void *table)
+{
+ struct page *page;
+
+ page = table;
+ call_rcu(&page->rcu_head, __tlb_remove_table_one_rcu);
+}
+#define __tlb_remove_table_one __tlb_remove_table_one
+#endif /* CONFIG_PT_RECLAIM */
+
static inline void invlpg(unsigned long addr)
{
asm volatile("invlpg (%0)" ::"r" (addr) : "memory");
}
+
#endif /* _ASM_X86_TLB_H */
--- a/arch/x86/kernel/paravirt.c~x86-mm-free-page-table-pages-by-rcu-instead-of-semi-rcu
+++ a/arch/x86/kernel/paravirt.c
@@ -59,10 +59,17 @@ void __init native_pv_lock_init(void)
static_branch_enable(&virt_spin_lock_key);
}
+#ifndef CONFIG_PT_RECLAIM
static void native_tlb_remove_table(struct mmu_gather *tlb, void *table)
{
tlb_remove_page(tlb, table);
}
+#else
+static void native_tlb_remove_table(struct mmu_gather *tlb, void *table)
+{
+ tlb_remove_table(tlb, table);
+}
+#endif
struct static_key paravirt_steal_enabled;
struct static_key paravirt_steal_rq_enabled;
--- a/arch/x86/mm/pgtable.c~x86-mm-free-page-table-pages-by-rcu-instead-of-semi-rcu
+++ a/arch/x86/mm/pgtable.c
@@ -19,12 +19,20 @@ EXPORT_SYMBOL(physical_mask);
#endif
#ifndef CONFIG_PARAVIRT
+#ifndef CONFIG_PT_RECLAIM
static inline
void paravirt_tlb_remove_table(struct mmu_gather *tlb, void *table)
{
tlb_remove_page(tlb, table);
}
-#endif
+#else
+static inline
+void paravirt_tlb_remove_table(struct mmu_gather *tlb, void *table)
+{
+ tlb_remove_table(tlb, table);
+}
+#endif /* !CONFIG_PT_RECLAIM */
+#endif /* !CONFIG_PARAVIRT */
gfp_t __userpte_alloc_gfp = GFP_PGTABLE_USER | PGTABLE_HIGHMEM;
--- a/include/linux/mm_types.h~x86-mm-free-page-table-pages-by-rcu-instead-of-semi-rcu
+++ a/include/linux/mm_types.h
@@ -438,7 +438,9 @@ FOLIO_MATCH(compound_head, _head_2a);
* struct ptdesc - Memory descriptor for page tables.
* @__page_flags: Same as page flags. Powerpc only.
* @pt_rcu_head: For freeing page table pages.
- * @pt_list: List of used page tables. Used for s390 and x86.
+ * @pt_list: List of used page tables. Used for s390 gmap shadow pages
+ * (which are not linked into the user page tables) and x86
+ * pgds.
* @_pt_pad_1: Padding that aliases with page's compound head.
* @pmd_huge_pte: Protected by ptdesc->ptl, used for THPs.
* @__page_mapping: Aliases with page->mapping. Unused for page tables.
--- a/mm/mmu_gather.c~x86-mm-free-page-table-pages-by-rcu-instead-of-semi-rcu
+++ a/mm/mmu_gather.c
@@ -311,11 +311,18 @@ static inline void tlb_table_invalidate(
}
}
-static void tlb_remove_table_one(void *table)
+#ifndef __tlb_remove_table_one
+static inline void __tlb_remove_table_one(void *table)
{
tlb_remove_table_sync_one();
__tlb_remove_table(table);
}
+#endif
+
+static void tlb_remove_table_one(void *table)
+{
+ __tlb_remove_table_one(table);
+}
static void tlb_table_flush(struct mmu_gather *tlb)
{
_
Patches currently in -mm which might be from zhengqi.arch@xxxxxxxxxxxxx are
mm-pgtable-make-ptep_clear-non-atomic.patch
mm-khugepaged-recheck-pmd-state-in-retract_page_tables.patch
mm-userfaultfd-recheck-dst_pmd-entry-in-move_pages_pte.patch
mm-introduce-zap_nonpresent_ptes.patch
mm-introduce-do_zap_pte_range.patch
mm-skip-over-all-consecutive-none-ptes-in-do_zap_pte_range.patch
mm-zap_install_uffd_wp_if_needed-return-whether-uffd-wp-pte-has-been-re-installed.patch
mm-do_zap_pte_range-return-any_skipped-information-to-the-caller.patch
mm-make-zap_pte_range-handle-full-within-pmd-range.patch
mm-pgtable-reclaim-empty-pte-page-in-madvisemadv_dontneed.patch
x86-mm-free-page-table-pages-by-rcu-instead-of-semi-rcu.patch
x86-select-arch_supports_pt_reclaim-if-x86_64.patch
