From: Jason Gunthorpe <jgg@ziepe.ca>
To: Hugh Dickins <hughd@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Gerald Schaefer <gerald.schaefer@linux.ibm.com>,
Vasily Gorbik <gor@linux.ibm.com>,
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Subject: Re: [PATCH v2 05/12] powerpc: add pte_free_defer() for pgtables sharing page
Date: Tue, 27 Jun 2023 14:01:11 -0300 [thread overview]
Message-ID: <ZJsV19f41CrfkFYa@ziepe.ca> (raw)
In-Reply-To: <c8284d0-91cb-b65e-4c95-bfeb627234f@google.com>
On Wed, Jun 21, 2023 at 07:36:11PM -0700, Hugh Dickins wrote:
> [PATCH v3 05/12] powerpc: add pte_free_defer() for pgtables sharing page
>
> Add powerpc-specific pte_free_defer(), to free table page via call_rcu().
> pte_free_defer() will be called inside khugepaged's retract_page_tables()
> loop, where allocating extra memory cannot be relied upon. This precedes
> the generic version to avoid build breakage from incompatible pgtable_t.
>
> This is awkward because the struct page contains only one rcu_head, but
> that page may be shared between PTE_FRAG_NR pagetables, each wanting to
> use the rcu_head at the same time. But powerpc never reuses a fragment
> once it has been freed: so mark the page Active in pte_free_defer(),
> before calling pte_fragment_free() directly; and there call_rcu() to
> pte_free_now() when last fragment is freed and the page is PageActive.
>
> Suggested-by: Jason Gunthorpe <jgg@ziepe.ca>
> Signed-off-by: Hugh Dickins <hughd@google.com>
> ---
> arch/powerpc/include/asm/pgalloc.h | 4 ++++
> arch/powerpc/mm/pgtable-frag.c | 29 ++++++++++++++++++++++++++---
> 2 files changed, 30 insertions(+), 3 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/pgalloc.h b/arch/powerpc/include/asm/pgalloc.h
> index 3360cad78ace..3a971e2a8c73 100644
> --- a/arch/powerpc/include/asm/pgalloc.h
> +++ b/arch/powerpc/include/asm/pgalloc.h
> @@ -45,6 +45,10 @@ static inline void pte_free(struct mm_struct *mm, pgtable_t ptepage)
> pte_fragment_free((unsigned long *)ptepage, 0);
> }
>
> +/* arch use pte_free_defer() implementation in arch/powerpc/mm/pgtable-frag.c */
> +#define pte_free_defer pte_free_defer
> +void pte_free_defer(struct mm_struct *mm, pgtable_t pgtable);
> +
> /*
> * Functions that deal with pagetables that could be at any level of
> * the table need to be passed an "index_size" so they know how to
> diff --git a/arch/powerpc/mm/pgtable-frag.c b/arch/powerpc/mm/pgtable-frag.c
> index 20652daa1d7e..0c6b68130025 100644
> --- a/arch/powerpc/mm/pgtable-frag.c
> +++ b/arch/powerpc/mm/pgtable-frag.c
> @@ -106,6 +106,15 @@ pte_t *pte_fragment_alloc(struct mm_struct *mm, int kernel)
> return __alloc_for_ptecache(mm, kernel);
> }
>
> +static void pte_free_now(struct rcu_head *head)
> +{
> + struct page *page;
> +
> + page = container_of(head, struct page, rcu_head);
> + pgtable_pte_page_dtor(page);
> + __free_page(page);
> +}
> +
> void pte_fragment_free(unsigned long *table, int kernel)
> {
> struct page *page = virt_to_page(table);
> @@ -115,8 +124,22 @@ void pte_fragment_free(unsigned long *table, int kernel)
>
> BUG_ON(atomic_read(&page->pt_frag_refcount) <= 0);
> if (atomic_dec_and_test(&page->pt_frag_refcount)) {
> - if (!kernel)
> - pgtable_pte_page_dtor(page);
> - __free_page(page);
> + if (kernel)
> + __free_page(page);
> + else if (TestClearPageActive(page))
> + call_rcu(&page->rcu_head, pte_free_now);
> + else
> + pte_free_now(&page->rcu_head);
> }
> }
> +
> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> +void pte_free_defer(struct mm_struct *mm, pgtable_t pgtable)
> +{
> + struct page *page;
> +
> + page = virt_to_page(pgtable);
> + SetPageActive(page);
> + pte_fragment_free((unsigned long *)pgtable, 0);
> +}
> +#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
Yes, this makes sense to me, very simple..
I always for get these details but atomic_dec_and_test() is a release?
So the SetPageActive is guarenteed to be visible in another thread
that reaches 0?
Thanks,
Jason
next prev parent reply other threads:[~2023-06-27 17:01 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-06-20 7:35 [PATCH v2 00/12] mm: free retracted page table by RCU Hugh Dickins
2023-06-20 7:40 ` [PATCH v2 01/12] mm/pgtable: add rcu_read_lock() and rcu_read_unlock()s Hugh Dickins
2023-06-20 7:42 ` [PATCH v2 02/12] mm/pgtable: add PAE safety to __pte_offset_map() Hugh Dickins
2023-06-20 7:43 ` [PATCH v2 03/12] arm: adjust_pte() use pte_offset_map_nolock() Hugh Dickins
2023-06-20 7:45 ` [PATCH v2 04/12] powerpc: assert_pte_locked() " Hugh Dickins
2023-06-20 7:47 ` [PATCH v2 05/12] powerpc: add pte_free_defer() for pgtables sharing page Hugh Dickins
2023-06-20 11:45 ` Jason Gunthorpe
2023-06-20 19:54 ` Hugh Dickins
2023-06-20 23:52 ` Jason Gunthorpe
2023-06-22 2:36 ` Hugh Dickins
2023-06-27 17:01 ` Jason Gunthorpe [this message]
2023-06-27 20:53 ` Hugh Dickins
2023-06-20 7:49 ` [PATCH v2 06/12] sparc: add pte_free_defer() for pte_t *pgtable_t Hugh Dickins
2023-06-20 7:51 ` [PATCH v2 07/12] s390: add pte_free_defer() for pgtables sharing page Hugh Dickins
2023-06-28 19:16 ` Gerald Schaefer
2023-06-29 5:08 ` Hugh Dickins
2023-06-29 15:22 ` Jason Gunthorpe
2023-06-29 15:56 ` Gerald Schaefer
2023-06-30 6:00 ` Hugh Dickins
2023-07-02 4:32 ` Hugh Dickins
2023-07-04 13:40 ` Alexander Gordeev
2023-07-04 16:03 ` Hugh Dickins
2023-07-04 15:19 ` Gerald Schaefer
2023-07-04 17:03 ` Hugh Dickins
2023-07-05 12:55 ` Gerald Schaefer
2023-07-06 1:20 ` Hugh Dickins
2023-07-06 15:02 ` Gerald Schaefer
2023-07-06 19:45 ` Hugh Dickins
2023-07-10 17:21 ` Jason Gunthorpe
2023-07-05 6:46 ` Alexander Gordeev
2023-07-06 0:52 ` Hugh Dickins
2023-07-07 14:37 ` Gerald Schaefer
2023-07-03 16:10 ` Gerald Schaefer
2023-06-29 13:59 ` Alexander Gordeev
2023-06-29 15:43 ` Gerald Schaefer
2023-06-30 13:38 ` Claudio Imbrenda
2023-06-30 15:28 ` Hugh Dickins
2023-06-30 16:25 ` Claudio Imbrenda
2023-06-30 19:22 ` Hugh Dickins
2023-07-03 11:00 ` Claudio Imbrenda
2023-07-03 21:29 ` Jason Gunthorpe
2023-06-20 7:53 ` [PATCH v2 08/12] mm/pgtable: add pte_free_defer() for pgtable as page Hugh Dickins
2023-06-20 7:54 ` [PATCH v2 09/12] mm/khugepaged: retract_page_tables() without mmap or vma lock Hugh Dickins
2023-06-20 7:56 ` [PATCH v2 10/12] mm/khugepaged: collapse_pte_mapped_thp() with mmap_read_lock() Hugh Dickins
2023-06-20 8:04 ` [PATCH mm " Hugh Dickins
2023-06-20 7:58 ` [PATCH v2 11/12] mm/khugepaged: delete khugepaged_collapse_pte_mapped_thps() Hugh Dickins
2023-06-20 7:59 ` [PATCH v2 12/12] mm: delete mmap_write_trylock() and vma_try_start_write() Hugh Dickins
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