lkml.org 
[lkml]   [2024]   [Feb]   [2]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH v5 23/25] arm64/mm: Implement pte_batch_hint()
Date
When core code iterates over a range of ptes and calls ptep_get() for
each of them, if the range happens to cover contpte mappings, the number
of pte reads becomes amplified by a factor of the number of PTEs in a
contpte block. This is because for each call to ptep_get(), the
implementation must read all of the ptes in the contpte block to which
it belongs to gather the access and dirty bits.

This causes a hotspot for fork(), as well as operations that unmap
memory such as munmap(), exit and madvise(MADV_DONTNEED). Fortunately we
can fix this by implementing pte_batch_hint() which allows their
iterators to skip getting the contpte tail ptes when gathering the batch
of ptes to operate on. This results in the number of PTE reads returning
to 1 per pte.

Tested-by: John Hubbard <jhubbard@nvidia.com>
Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
---
arch/arm64/include/asm/pgtable.h | 9 +++++++++
1 file changed, 9 insertions(+)

diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index ad04adb7b87f..353ea67b5d75 100644
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h
@@ -1220,6 +1220,15 @@ static inline void contpte_try_unfold(struct mm_struct *mm, unsigned long addr,
__contpte_try_unfold(mm, addr, ptep, pte);
}

+#define pte_batch_hint pte_batch_hint
+static inline unsigned int pte_batch_hint(pte_t *ptep, pte_t pte)
+{
+ if (!pte_valid_cont(pte))
+ return 1;
+
+ return CONT_PTES - (((unsigned long)ptep >> 3) & (CONT_PTES - 1));
+}
+
/*
* The below functions constitute the public API that arm64 presents to the
* core-mm to manipulate PTE entries within their page tables (or at least this
--
2.25.1

\
 
 \ /
  Last update: 2024-05-27 14:45    [W:0.613 / U:0.036 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site