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Message-ID: <c02c31eb-7063-510f-2c2d-8d18a6bb5eee@infradead.org>
Date: Tue, 12 Jan 2021 13:15:12 -0800
From: Randy Dunlap <rdunlap@...radead.org>
To: "Liam R. Howlett" <Liam.Howlett@...cle.com>,
maple-tree@...ts.infradead.org, linux-mm@...ck.org,
linux-kernel@...r.kernel.org
Cc: Andrew Morton <akpm@...gle.com>, Song Liu <songliubraving@...com>,
Davidlohr Bueso <dave@...olabs.net>,
"Paul E . McKenney" <paulmck@...nel.org>,
Matthew Wilcox <willy@...radead.org>,
Jerome Glisse <jglisse@...hat.com>,
David Rientjes <rientjes@...gle.com>,
Axel Rasmussen <axelrasmussen@...gle.com>,
Suren Baghdasaryan <surenb@...gle.com>,
Vlastimil Babka <vbabka@...e.cz>,
Rik van Riel <riel@...riel.com>,
Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH v2 14/70] mm/mmap: Change do_brk_flags() to expand
existing VMA and add do_brk_munmap()
Hi--
On 1/12/21 8:11 AM, Liam R. Howlett wrote:
> Avoid allocating a new VMA when it is not necessary. Expand or contract
> the existing VMA instead. This avoids unnecessary tree manipulations
> and allocations.
>
> Once the VMA is known, use it directly when populating to avoid
> unnecessary lookup work.
>
> Signed-off-by: Liam R. Howlett <Liam.Howlett@...cle.com>
> ---
> mm/mmap.c | 299 +++++++++++++++++++++++++++++++++++++++++++-----------
> 1 file changed, 237 insertions(+), 62 deletions(-)
>
> diff --git a/mm/mmap.c b/mm/mmap.c
> index a2b32202191d6..f500d5e490f1c 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -2022,8 +2068,7 @@ 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. May return
> - * NULL in the case of no vma at addr or above
> + * find_vma() - Find the VMA for a given address, or the next vma.
> * @mm The mm_struct to check
* @mm: ...
> * @addr: The address
> *
> @@ -2777,16 +2825,102 @@ SYSCALL_DEFINE5(remap_file_pages, unsigned long, start, unsigned long, size,
> }
>
> /*
> - * this is really a simplified "do_mmap". it only handles
> - * anonymous maps. eventually we may be able to do some
> - * brk-specific accounting here.
> + * bkr_munmap() - Unmap a parital vma.
> + * @mas: The maple tree state.
> + * @vma: The vma to be modified
> + * @newbrk: the start of the address to unmap
> + * @oldbrk: The end of the address to unmap
missing:
* @uf: ...
> + *
> + * Returns: 0 on success.
> + * unmaps a partial VMA mapping. Does not handle alignment, downgrades lock if
> + * possible.
> */
> -static int do_brk_flags(unsigned long addr, unsigned long len,
> - unsigned long flags, struct list_head *uf)
> +static int do_brk_munmap(struct ma_state *mas, struct vm_area_struct *vma,
> + unsigned long newbrk, unsigned long oldbrk,
> + struct list_head *uf)
> +{
> + struct mm_struct *mm = vma->vm_mm;
> + struct vm_area_struct unmap;
> + unsigned long unmap_pages;
> + int ret = 1;
> +
> + arch_unmap(mm, newbrk, oldbrk);
> +
> + if (likely(vma->vm_start >= newbrk)) { // remove entire mapping(s)
> + mas_set(mas, newbrk);
> + if (vma->vm_start != newbrk)
> + mas_reset(mas); // cause a re-walk for the first overlap.
> + ret = do_mas_munmap(mas, mm, newbrk, oldbrk-newbrk, uf, true);
> + goto munmap_full_vma;
> + }
> +
> + vma_init(&unmap, mm);
> + unmap.vm_start = newbrk;
> + unmap.vm_end = oldbrk;
> + ret = userfaultfd_unmap_prep(&unmap, newbrk, oldbrk, uf);
> + if (ret)
> + return ret;
> + ret = 1;
> +
> + // Change the oldbrk of vma to the newbrk of the munmap area
> + vma_adjust_trans_huge(vma, vma->vm_start, newbrk, 0);
> + if (vma->anon_vma) {
> + anon_vma_lock_write(vma->anon_vma);
> + anon_vma_interval_tree_pre_update_vma(vma);
> + }
> +
> + vma->vm_end = newbrk;
> + if (vma_mas_remove(&unmap, mas))
> + goto mas_store_fail;
> +
> + vmacache_invalidate(vma->vm_mm);
> + if (vma->anon_vma) {
> + anon_vma_interval_tree_post_update_vma(vma);
> + anon_vma_unlock_write(vma->anon_vma);
> + }
> +
> + unmap_pages = vma_pages(&unmap);
> + if (unmap.vm_flags & VM_LOCKED) {
> + mm->locked_vm -= unmap_pages;
> + munlock_vma_pages_range(&unmap, newbrk, oldbrk);
> + }
> +
> + mmap_write_downgrade(mm);
> + unmap_region(mm, &unmap, vma, newbrk, oldbrk);
> + /* Statistics */
> + vm_stat_account(mm, unmap.vm_flags, -unmap_pages);
> + if (unmap.vm_flags & VM_ACCOUNT)
> + vm_unacct_memory(unmap_pages);
> +
> +munmap_full_vma:
> + validate_mm_mt(mm);
> + return ret;
> +
> +mas_store_fail:
> + vma->vm_end = oldbrk;
> + anon_vma_interval_tree_post_update_vma(vma);
> + anon_vma_unlock_write(vma->anon_vma);
> + return -ENOMEM;
> +}
> +
> +/*
> + * do_brk_flags() - Increase the brk vma if the flags match.
> + * @mas: The maple tree state.
> + * @addr: The start address
> + * @len: The length of the increase
> + * @vma: The vma,
s/@.../@...vma/ ??
> + * @flags: The VMA Flags
> + *
> + * Extend the brk VMA from addr to addr + len. If the VMA is NULL or the flags
> + * do not match then create a new anonymous VMA. Eventually we may be able to
> + * do some brk-specific accounting here.
> + */
> +static int do_brk_flags(struct ma_state *mas, struct vm_area_struct **brkvma,
> + unsigned long addr, unsigned long len,
> + unsigned long flags)
> {
> struct mm_struct *mm = current->mm;
> - struct vm_area_struct *vma, *prev;
> - pgoff_t pgoff = addr >> PAGE_SHIFT;
> + struct vm_area_struct *prev = NULL, *vma;
> int error;
> unsigned long mapped_addr;
> validate_mm_mt(mm);
thanks.
--
~Randy
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