On 2025/1/3 16:02, Kevin Brodsky wrote:
On 03/01/2025 04:48, Qi Zheng wrote:
Hi Kevin,
On 2025/1/3 00:53, Kevin Brodsky wrote:
On 30/12/2024 10:07, Qi Zheng wrote:
static inline void riscv_tlb_remove_ptdesc(struct mmu_gather *tlb,
void *pt)
{
- if (riscv_use_sbi_for_rfence())
+ if (riscv_use_sbi_for_rfence()) {
tlb_remove_ptdesc(tlb, pt);
- else
+ } else {
+ pagetable_dtor(pt);
tlb_remove_page_ptdesc(tlb, pt);
I find the imbalance pretty confusing: pagetable_dtor() is called
explicitly before using tlb_remove_page() but not tlb_remove_ptdesc().
Doesn't that assume that CONFIG_MMU_GATHER_HAVE_TABLE_FREE is selected?
Could we not call pagetable_dtor() from __tlb_batch_free_encoded_pages()
to ensure that the dtor is always called just before freeing, and remove
In __tlb_batch_free_encoded_pages(), we can indeed detect PageTable()
and call pagetable_dtor() to dtor the page table pages.
But __tlb_batch_free_encoded_pages() is also used to free normal pages
(not page table pages), so I don't want to add overhead there.
Interesting, can a tlb batch refer to pages than are not PTPs then?
Yes, you can see the caller of __tlb_remove_folio_pages() or
tlb_remove_page_size().
But now I think maybe we can do this in tlb_remove_page_ptdesc(), like
this:
diff --git a/arch/csky/include/asm/pgalloc.h
b/arch/csky/include/asm/pgalloc.h
index f1ce5b7b28f22..e45c7e91dcbf9 100644
--- a/arch/csky/include/asm/pgalloc.h
+++ b/arch/csky/include/asm/pgalloc.h
@@ -63,7 +63,6 @@ static inline pgd_t *pgd_alloc(struct mm_struct *mm)
#define __pte_free_tlb(tlb, pte, address) \
do { \
- pagetable_dtor(page_ptdesc(pte)); \
tlb_remove_page_ptdesc(tlb, page_ptdesc(pte)); \
} while (0)
[...]
diff --git a/include/asm-generic/tlb.h b/include/asm-generic/tlb.h
index a96d4b440f3da..a59205863f431 100644
--- a/include/asm-generic/tlb.h
+++ b/include/asm-generic/tlb.h
@@ -506,6 +506,7 @@ static inline void tlb_remove_ptdesc(struct
mmu_gather *tlb, void *pt)
/* Like tlb_remove_ptdesc, but for page-like page directories. */
static inline void tlb_remove_page_ptdesc(struct mmu_gather *tlb,
struct ptdesc *pt)
{
+ pagetable_dtor(pt);
tlb_remove_page(tlb, ptdesc_page(pt));
}
I think this is an interesting idea, it does make arch code easier to
follow. OTOH it would have been more natural to me to call
pagetable_dtor() from tlb_remove_page(). I can however see that this
doesn't work, because tlb_remove_table() is defined as tlb_remove_page()
if CONFIG_MMU_GATHER_HAVE_TABLE_FREE isn't selected. Which brings me
back to my earlier question: in that case, aren't we missing a call to
pagetable_dtor() when using tlb_remove_table() (or tlb_remove_ptdesc())?
Thank you for pointing this out!
Now, there are the following architectures selected
CONFIG_MMU_GATHER_RCU_TABLE_FREE:
1. arm: select MMU_GATHER_RCU_TABLE_FREE if SMP && ARM_LPAE
2. arm64: select MMU_GATHER_RCU_TABLE_FREE
3. powerpc: select MMU_GATHER_RCU_TABLE_FREE
4. riscv: select MMU_GATHER_RCU_TABLE_FREE if SMP && MMU
5. s390: select MMU_GATHER_RCU_TABLE_FREE
6. sparc: select MMU_GATHER_RCU_TABLE_FREE if SMP
7. x86: select MMU_GATHER_RCU_TABLE_FREE if PARAVIRT
If CONFIG_MMU_GATHER_TABLE_FREE is selected, an architecture is expected
to provide __tlb_remove_table(). This patch series modifies the
__tlb_remove_table() in arm, arm64, riscv, s390 and x86. Among them,
arm64 and s390 unconditionally select MMU_GATHER_RCU_TABLE_FREE, so we
only need to double-check arm, riscv and x86.
For x86, it was called tlb_remove_page() in the non-PARAVIRT case, and I
added pagetable_dtor() for it explicitly (see patch #11), so this should
be no problem.
For riscv, it will only call tlb_remove_ptdesc() in the case of
SMP && MMU, so this should be no problem.
For arm, the call to pagetable_dtor() is indeed missed in the
non-MMU_GATHER_RCU_TABLE_FREE case. This needs to be fixed. But we
can't fix this by adding pagetable_dtor() to tlb_remove_table(),
because some architectures call tlb_remove_table() but don't support
page table statistics, like sparc.
So a more direct fix might be:
diff --git a/include/asm-generic/tlb.h b/include/asm-generic/tlb.h
index a59205863f431..0a131444a18ca 100644
--- a/include/asm-generic/tlb.h
+++ b/include/asm-generic/tlb.h
@@ -500,6 +500,9 @@ static inline void tlb_remove_page(struct mmu_gather
*tlb, struct page *page)
static inline void tlb_remove_ptdesc(struct mmu_gather *tlb, void *pt)
{
+#ifndef CONFIG_MMU_GATHER_TABLE_FREE
+ pagetable_dtor(pt);
+#endif
tlb_remove_table(tlb, pt);
}
Or fix it directly in arm? Like the following:
diff --git a/arch/arm/include/asm/tlb.h b/arch/arm/include/asm/tlb.h
index ea4fbe7b17f6f..cf5d0ca021440 100644
--- a/arch/arm/include/asm/tlb.h
+++ b/arch/arm/include/asm/tlb.h
@@ -43,6 +43,9 @@ __pte_free_tlb(struct mmu_gather *tlb, pgtable_t pte,
unsigned long addr)
__tlb_adjust_range(tlb, addr - PAGE_SIZE, 2 * PAGE_SIZE);
#endif
+#ifndef CONFIG_MMU_GATHER_TABLE_FREE
+ pagetable_dtor(ptdesc);
+#endif
tlb_remove_ptdesc(tlb, ptdesc);
}
Thanks,
Qi
- Kevin
