[RFC PATCH v12 based on mm-unstable as of Feb 21, 2025 20/25] mm, fs: skip tlb flushes for luf'd filemap that already has been done

Byungchul Park
2025-02-26T12:01:54Z

For luf'd filemap, tlb shootdown is performed when updating page cache,
no matter whether tlb flushes required already has been done or not.

By storing luf meta data in struct address_space and updating the luf
meta data properly, we can skip unnecessary tlb flush.

Signed-off-by: Byungchul Park <byungchul@sk.com>
---
fs/inode.c | 1 +
include/linux/fs.h | 4 ++-
include/linux/mm_types.h | 2 ++
mm/memory.c | 4 +--
mm/rmap.c | 59 +++++++++++++++++++++++++---------------
mm/truncate.c | 14 +++++-----
mm/vmscan.c | 2 +-
7 files changed, 53 insertions(+), 33 deletions(-)

diff --git a/fs/inode.c b/fs/inode.c
index 5587aabdaa5ee..752fb2df6f3b3 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -475,6 +475,7 @@ static void __address_space_init_once(struct address_space *mapping)
init_rwsem(&mapping->i_mmap_rwsem);
INIT_LIST_HEAD(&mapping->i_private_list);
spin_lock_init(&mapping->i_private_lock);
+ luf_batch_init(&mapping->luf_batch);
mapping->i_mmap = RB_ROOT_CACHED;
}

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 78aaf769d32d1..a2f014b31028f 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -498,6 +498,7 @@ extern const struct address_space_operations empty_aops;
* @i_private_lock: For use by the owner of the address_space.
* @i_private_list: For use by the owner of the address_space.
* @i_private_data: For use by the owner of the address_space.
+ * @luf_batch: Data to track need of tlb flush by luf.
*/
struct address_space {
struct inode *host;
@@ -519,6 +520,7 @@ struct address_space {
struct list_head i_private_list;
struct rw_semaphore i_mmap_rwsem;
void * i_private_data;
+ struct luf_batch luf_batch;
} __attribute__((aligned(sizeof(long)))) __randomize_layout;
/*
* On most architectures that alignment is already the case; but
@@ -545,7 +547,7 @@ static inline int mapping_write_begin(struct file *file,
* Ensure to clean stale tlb entries for this mapping.
*/
if (!ret)
- luf_flush(0);
+ luf_flush_mapping(mapping);

return ret;
}
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index c32ef19a25056..d73a3eb0f7b21 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -1362,10 +1362,12 @@ extern void tlb_finish_mmu(struct mmu_gather *tlb);
void luf_flush(unsigned short luf_key);
void luf_flush_mm(struct mm_struct *mm);
void luf_flush_vma(struct vm_area_struct *vma);
+void luf_flush_mapping(struct address_space *mapping);
#else
static inline void luf_flush(unsigned short luf_key) {}
static inline void luf_flush_mm(struct mm_struct *mm) {}
static inline void luf_flush_vma(struct vm_area_struct *vma) {}
+static inline void luf_flush_mapping(struct address_space *mapping) {}
#endif

struct vm_fault;
diff --git a/mm/memory.c b/mm/memory.c
index 93e5879583b07..62137ab258d2c 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -6296,10 +6296,10 @@ vm_fault_t handle_mm_fault(struct vm_area_struct *vma, unsigned long address,
if (flush) {
/*
* If it has a VM_SHARED mapping, all the mms involved
- * should be luf_flush'ed.
+ * in the struct address_space should be luf_flush'ed.
*/
if (mapping)
- luf_flush(0);
+ luf_flush_mapping(mapping);
luf_flush_mm(mm);
}

diff --git a/mm/rmap.c b/mm/rmap.c
index fe9c4606ae542..f5c5190be24e0 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -691,7 +691,7 @@ void fold_batch(struct tlbflush_unmap_batch *dst,
#define NR_LUF_BATCH (1 << (sizeof(short) * 8))

/*
- * Use 0th entry as accumulated batch.
+ * XXX: Reserve the 0th entry for later use.
*/
struct luf_batch luf_batch[NR_LUF_BATCH];

@@ -936,7 +936,7 @@ void luf_flush_vma(struct vm_area_struct *vma)
mapping = vma->vm_file->f_mapping;

if (mapping)
- luf_flush(0);
+ luf_flush_mapping(mapping);
luf_flush_mm(mm);
}

@@ -962,6 +962,29 @@ void luf_flush_mm(struct mm_struct *mm)
try_to_unmap_flush();
}

+void luf_flush_mapping(struct address_space *mapping)
+{
+ struct tlbflush_unmap_batch *tlb_ubc = &current->tlb_ubc;
+ struct luf_batch *lb;
+ unsigned long flags;
+ unsigned long lb_ugen;
+
+ if (!mapping)
+ return;
+
+ lb = &mapping->luf_batch;
+ read_lock_irqsave(&lb->lock, flags);
+ fold_batch(tlb_ubc, &lb->batch, false);
+ lb_ugen = lb->ugen;
+ read_unlock_irqrestore(&lb->lock, flags);
+
+ if (arch_tlbbatch_diet(&tlb_ubc->arch, lb_ugen))
+ return;
+
+ try_to_unmap_flush();
+}
+EXPORT_SYMBOL(luf_flush_mapping);
+
/*
* Flush TLB entries for recently unmapped pages from remote CPUs. It is
* important if a PTE was dirty when it was unmapped that it's flushed
@@ -1010,7 +1033,8 @@ void try_to_unmap_flush_dirty(void)

static void set_tlb_ubc_flush_pending(struct mm_struct *mm, pte_t pteval,
unsigned long start, unsigned long end,
- struct vm_area_struct *vma)
+ struct vm_area_struct *vma,
+ struct address_space *mapping)
{
struct tlbflush_unmap_batch *tlb_ubc;
int batch;
@@ -1032,27 +1056,15 @@ static void set_tlb_ubc_flush_pending(struct mm_struct *mm, pte_t pteval,
tlb_ubc = &current->tlb_ubc;
else {
tlb_ubc = &current->tlb_ubc_ro;
+
fold_luf_batch_mm(&mm->luf_batch, mm);
+ if (mapping)
+ fold_luf_batch_mm(&mapping->luf_batch, mm);
}

arch_tlbbatch_add_pending(&tlb_ubc->arch, mm, start, end);
tlb_ubc->flush_required = true;

- if (can_luf_test()) {
- struct luf_batch *lb;
- unsigned long flags;
-
- /*
- * Accumulate to the 0th entry right away so that
- * luf_flush(0) can be uesed to properly perform pending
- * TLB flush once this unmapping is observed.
- */
- lb = &luf_batch[0];
- write_lock_irqsave(&lb->lock, flags);
- __fold_luf_batch(lb, tlb_ubc, new_luf_ugen());
- write_unlock_irqrestore(&lb->lock, flags);
- }
-
/*
* Ensure compiler does not re-order the setting of tlb_flush_batched
* before the PTE is cleared.
@@ -1134,7 +1146,8 @@ void flush_tlb_batched_pending(struct mm_struct *mm)
#else
static void set_tlb_ubc_flush_pending(struct mm_struct *mm, pte_t pteval,
unsigned long start, unsigned long end,
- struct vm_area_struct *vma)
+ struct vm_area_struct *vma,
+ struct address_space *mapping)
{
}

@@ -1511,7 +1524,7 @@ int folio_mkclean(struct folio *folio)
/*
* Ensure to clean stale tlb entries for this mapping.
*/
- luf_flush(0);
+ luf_flush_mapping(mapping);

return cleaned;
}
@@ -2198,6 +2211,7 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
unsigned long nr_pages = 1, end_addr;
unsigned long pfn;
unsigned long hsz = 0;
+ struct address_space *mapping = folio_mapping(folio);

/*
* When racing against e.g. zap_pte_range() on another cpu,
@@ -2359,7 +2373,7 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
* and traps if the PTE is unmapped.
*/
if (should_defer_flush(mm, flags))
- set_tlb_ubc_flush_pending(mm, pteval, address, end_addr, vma);
+ set_tlb_ubc_flush_pending(mm, pteval, address, end_addr, vma, mapping);
else
flush_tlb_range(vma, address, end_addr);
if (pte_dirty(pteval))
@@ -2611,6 +2625,7 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma,
enum ttu_flags flags = (enum ttu_flags)(long)arg;
unsigned long pfn;
unsigned long hsz = 0;
+ struct address_space *mapping = folio_mapping(folio);

/*
* When racing against e.g. zap_pte_range() on another cpu,
@@ -2758,7 +2773,7 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma,
*/
pteval = ptep_get_and_clear(mm, address, pvmw.pte);

- set_tlb_ubc_flush_pending(mm, pteval, address, address + PAGE_SIZE, vma);
+ set_tlb_ubc_flush_pending(mm, pteval, address, address + PAGE_SIZE, vma, mapping);
} else {
pteval = ptep_clear_flush(vma, address, pvmw.pte);
}
diff --git a/mm/truncate.c b/mm/truncate.c
index 68c9ded2f789b..8c133b93cefe8 100644
--- a/mm/truncate.c
+++ b/mm/truncate.c
@@ -142,7 +142,7 @@ void folio_invalidate(struct folio *folio, size_t offset, size_t length)
/*
* Ensure to clean stale tlb entries for this mapping.
*/
- luf_flush(0);
+ luf_flush_mapping(folio->mapping);
}
EXPORT_SYMBOL_GPL(folio_invalidate);

@@ -183,7 +183,7 @@ int truncate_inode_folio(struct address_space *mapping, struct folio *folio)
/*
* Ensure to clean stale tlb entries for this mapping.
*/
- luf_flush(0);
+ luf_flush_mapping(mapping);
return 0;
}

@@ -234,7 +234,7 @@ bool truncate_inode_partial_folio(struct folio *folio, loff_t start, loff_t end)
/*
* Ensure to clean stale tlb entries for this mapping.
*/
- luf_flush(0);
+ luf_flush_mapping(folio->mapping);

if (!folio_test_large(folio))
return true;
@@ -324,7 +324,7 @@ long mapping_evict_folio(struct address_space *mapping, struct folio *folio)
/*
* Ensure to clean stale tlb entries for this mapping.
*/
- luf_flush(0);
+ luf_flush_mapping(mapping);

return ret;
}
@@ -459,7 +459,7 @@ void truncate_inode_pages_range(struct address_space *mapping,
/*
* Ensure to clean stale tlb entries for this mapping.
*/
- luf_flush(0);
+ luf_flush_mapping(mapping);
}
EXPORT_SYMBOL(truncate_inode_pages_range);

@@ -579,7 +579,7 @@ unsigned long mapping_try_invalidate(struct address_space *mapping,
/*
* Ensure to clean stale tlb entries for this mapping.
*/
- luf_flush(0);
+ luf_flush_mapping(mapping);
return count;
}

@@ -749,7 +749,7 @@ int invalidate_inode_pages2_range(struct address_space *mapping,
/*
* Ensure to clean stale tlb entries for this mapping.
*/
- luf_flush(0);
+ luf_flush_mapping(mapping);
return ret;
}
EXPORT_SYMBOL_GPL(invalidate_inode_pages2_range);
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 422b9a03a6753..f145c09629b97 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -853,7 +853,7 @@ long remove_mapping(struct address_space *mapping, struct folio *folio)
/*
* Ensure to clean stale tlb entries for this mapping.
*/
- luf_flush(0);
+ luf_flush_mapping(mapping);

return ret;
}
--
2.17.1