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Date: Thu, 13 Jan 2022 16:53:42 +0100
From: Vlastimil Babka <vbabka@...e.cz>
To: Liam Howlett <liam.howlett@...cle.com>,
"maple-tree@...ts.infradead.org" <maple-tree@...ts.infradead.org>,
"linux-mm@...ck.org" <linux-mm@...ck.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
Andrew Morton <akpm@...ux-foundation.org>
Cc: Song Liu <songliubraving@...com>,
Davidlohr Bueso <dave@...olabs.net>,
"Paul E . McKenney" <paulmck@...nel.org>,
Matthew Wilcox <willy@...radead.org>,
Laurent Dufour <ldufour@...ux.ibm.com>,
David Rientjes <rientjes@...gle.com>,
Axel Rasmussen <axelrasmussen@...gle.com>,
Suren Baghdasaryan <surenb@...gle.com>,
Rik van Riel <riel@...riel.com>,
Peter Zijlstra <peterz@...radead.org>,
Michel Lespinasse <walken.cr@...il.com>,
Jerome Glisse <jglisse@...hat.com>,
Minchan Kim <minchan@...gle.com>,
Joel Fernandes <joelaf@...gle.com>,
Rom Lemarchand <romlem@...gle.com>
Subject: Re: [PATCH v4 22/66] mm: Use maple tree operations for
find_vma_intersection() and find_vma()
On 12/1/21 15:29, Liam Howlett wrote:
> From: "Liam R. Howlett" <Liam.Howlett@...cle.com>
>
> Move find_vma_intersection() to mmap.c and change implementation to
> maple tree.
>
> When searching for a vma within a range, it is easier to use the maple
> tree interface. This means the find_vma() call changes to a special
> case of the find_vma_intersection().
>
> Exported for kvm module.
>
> Signed-off-by: Liam R. Howlett <Liam.Howlett@...cle.com>
> ---
> include/linux/mm.h | 25 ++++++-------------------
> mm/mmap.c | 38 ++++++++++++++++++++++++++++----------
> 2 files changed, 34 insertions(+), 29 deletions(-)
>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index c08f6d541b8a..39a947f29f6d 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -2812,26 +2812,13 @@ extern struct vm_area_struct * find_vma(struct mm_struct * mm, unsigned long add
> extern struct vm_area_struct * find_vma_prev(struct mm_struct * mm, unsigned long addr,
> struct vm_area_struct **pprev);
>
> -/**
> - * find_vma_intersection() - Look up the first VMA which intersects the interval
> - * @mm: The process address space.
> - * @start_addr: The inclusive start user address.
> - * @end_addr: The exclusive end user address.
> - *
> - * Returns: The first VMA within the provided range, %NULL otherwise. Assumes
> - * start_addr < end_addr.
> +/*
> + * Look up the first VMA which intersects the interval [start_addr, end_addr)
> + * NULL if none. Assume start_addr < end_addr.
> */
> -static inline
> -struct vm_area_struct *find_vma_intersection(struct mm_struct *mm,
> - unsigned long start_addr,
> - unsigned long end_addr)
> -{
> - struct vm_area_struct *vma = find_vma(mm, start_addr);
> -
> - if (vma && end_addr <= vma->vm_start)
> - vma = NULL;
> - return vma;
> -}
> +extern struct vm_area_struct *find_vma_intersection(struct mm_struct *mm,
> + unsigned long start_addr,
> + unsigned long end_addr);
>
> /**
> * vma_lookup() - Find a VMA at a specific address
> diff --git a/mm/mmap.c b/mm/mmap.c
> index e4c8ce377f2c..c06c5b850e1e 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -2003,29 +2003,47 @@ get_unmapped_area(struct file *file, unsigned long addr, unsigned long len,
> EXPORT_SYMBOL(get_unmapped_area);
>
> /**
> - * find_vma() - Find the VMA for a given address, or the next vma.
> - * @mm: The mm_struct to check
> - * @addr: The address
> + * find_vma_intersection() - Look up the first VMA which intersects the interval
> + * @mm: The process address space.
> + * @start_addr: The inclusive start user address.
> + * @end_addr: The exclusive end user address.
> *
> - * Returns: The VMA associated with addr, or the next vma.
> - * May return %NULL in the case of no vma at addr or above.
> + * Returns: The first VMA within the provided range, %NULL otherwise. Assumes
> + * start_addr < end_addr.
> */
> -struct vm_area_struct *find_vma(struct mm_struct *mm, unsigned long addr)
> +struct vm_area_struct *find_vma_intersection(struct mm_struct *mm,
> + unsigned long start_addr,
> + unsigned long end_addr)
> {
> struct vm_area_struct *vma;
> - MA_STATE(mas, &mm->mm_mt, addr, addr);
> + MA_STATE(mas, &mm->mm_mt, start_addr, start_addr);
>
> mmap_assert_locked(mm);
> /* Check the cache first. */
> - vma = vmacache_find(mm, addr);
> + vma = vmacache_find(mm, start_addr);
> if (likely(vma))
> return vma;
>
> - vma = mas_find(&mas, -1);
> + vma = mas_find(&mas, end_addr - 1);
> if (vma)
> - vmacache_update(addr, vma);
> + vmacache_update(mas.index, vma);
> return vma;
> }
> +EXPORT_SYMBOL(find_vma_intersection);
> +
> +/**
> + * find_vma() - Find the VMA for a given address, or the next vma.
> + * @mm: The mm_struct to check
> + * @addr: The address
> + *
> + * Returns: The VMA associated with addr, or the next vma.
> + * May return NULL in the case of no vma at addr or above.
> + */
> +inline struct vm_area_struct *find_vma(struct mm_struct *mm, unsigned long addr)
I think the inline does nothing here (except maybe for LTO builds). Callers
will do a function call to find_vma() and then probably that causes another
function call (likely a tail call) to find_vma_intersection().
You'd have to put this definition of find_vma() to include/linux/mm.h to
make the callers inline it and just add the 0 parameter before doing a
function call of find_vma_intersection() - which would make sense.
> +{
> + // Note find_vma_intersection will decrease 0 to underflow to ULONG_MAX
Nit: this comment syntax using //.
> + return find_vma_intersection(mm, addr, 0);
> +}
> EXPORT_SYMBOL(find_vma);
>
> /**
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