Re: [PATCH v4 10/15] riscv: pgtable: move pagetable_dtor() to __tlb_remove_table()
From: Kevin Brodsky <hidden>
Date: 2025-01-03 13:27:11
Also in:
linux-arch, linux-arm-kernel, linux-m68k, linux-mips, linux-mm, linux-riscv, linux-s390, linux-sh, linux-um, lkml, loongarch, sparclinux
On 03/01/2025 10:35, Qi Zheng wrote:
On 2025/1/3 17:13, Qi Zheng wrote:quoted
On 2025/1/3 16:02, Kevin Brodsky wrote:quoted
On 03/01/2025 04:48, Qi Zheng wrote:quoted
[...] 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().
I had a brief look but clearly not a good enough one! I hadn't realised that "table" in tlb_remove_table() means PTP, while "page" in tlb_remove_page() can mean any page, and it's making more sense now. [...]
quoted
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.
When I investigated this for my own series, I found that the only case where ctor/dtor are not called for page-sized page tables is 32-bit sparc (see table at the end of [1]). However only 64-bit sparc makes use of tlb_remove_table() (at PTE level, where ctor/dtor are already called). So really calling pagetable_dtor() from tlb_remove_table() in the non-MMU_GATHER_TABLE_FREE case seems to be the obvious thing to do. Once this is done, we should be able to replace all those confusing calls to tlb_remove_page() on PTPs with tlb_remove_table() and remove the explicit call to pagetable_dtor(). AIUI this is essentially what Peter suggested on v3 [2]. [1] https://lore.kernel.org/linux-mm/20241219164425.2277022-1-kevin.brodsky@arm.com/ (local) [2] https://lore.kernel.org/linux-mm/20250103111457.GC22934@noisy.programming.kicks-ass.net/ (local) [...]
quoted hunk ↗ jump to hunk
Or can we just not let tlb_remove_table() fall back to tlb_remove_page()? Like the following:diff --git a/include/asm-generic/tlb.h b/include/asm-generic/tlb.h index a59205863f431..354ffaa4bd120 100644 --- a/include/asm-generic/tlb.h +++ b/include/asm-generic/tlb.h@@ -195,8 +195,6 @@* various ptep_get_and_clear() functions. */ -#ifdef CONFIG_MMU_GATHER_TABLE_FREE - struct mmu_table_batch { #ifdef CONFIG_MMU_GATHER_RCU_TABLE_FREE struct rcu_head rcu;@@ -219,16 +217,6 @@ static inline void __tlb_remove_table(void *table)extern void tlb_remove_table(struct mmu_gather *tlb, void *table); -#else /* !CONFIG_MMU_GATHER_HAVE_TABLE_FREE */ - -/* - * Without MMU_GATHER_TABLE_FREE the architecture is assumed to have page based - * page directories and we can use the normal page batching to free them. - */ -#define tlb_remove_table(tlb, page) tlb_remove_page((tlb), (page))
We still need a different implementation of tlb_remove_table() in this
case. We could define it inline here:
static inline void tlb_remove_table(struct mmu_gather *tlb, void *table)
{
struct page *page = table;
pagetable_dtor(page_ptdesc(page));
tlb_remove_page(page);
}
- Kevin