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Message-Id: <32ce6f0e-2c48-a54f-9839-baf7d11c48fe@linux.vnet.ibm.com>
Date: Tue, 24 Jul 2018 18:22:06 +0200
From: Laurent Dufour <ldufour@...ux.vnet.ibm.com>
To: Yang Shi <yang.shi@...ux.alibaba.com>, mhocko@...nel.org,
willy@...radead.org, kirill@...temov.name,
akpm@...ux-foundation.org
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC v5 PATCH 1/2] mm: refactor do_munmap() to extract the common
part
On 19/07/2018 01:21, Yang Shi wrote:
> Introduces three new helper functions:
> * munmap_addr_sanity()
> * munmap_lookup_vma()
> * munmap_mlock_vma()
>
> They will be used by do_munmap() and the new do_munmap with zapping
> large mapping early in the later patch.
>
> There is no functional change, just code refactor.
>
> Signed-off-by: Yang Shi <yang.shi@...ux.alibaba.com>
FWIW : Reviewed-by : Laurent Dufour <ldufour@...ux.vnet.ibm.com>
> ---
> mm/mmap.c | 120 ++++++++++++++++++++++++++++++++++++++++++--------------------
> 1 file changed, 82 insertions(+), 38 deletions(-)
>
> diff --git a/mm/mmap.c b/mm/mmap.c
> index d1eb87e..2504094 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -2686,34 +2686,44 @@ int split_vma(struct mm_struct *mm, struct vm_area_struct *vma,
> return __split_vma(mm, vma, addr, new_below);
> }
>
> -/* Munmap is split into 2 main parts -- this part which finds
> - * what needs doing, and the areas themselves, which do the
> - * work. This now handles partial unmappings.
> - * Jeremy Fitzhardinge <jeremy@...p.org>
> - */
> -int do_munmap(struct mm_struct *mm, unsigned long start, size_t len,
> - struct list_head *uf)
> +static inline bool munmap_addr_sanity(unsigned long start, size_t len)
> {
> - unsigned long end;
> - struct vm_area_struct *vma, *prev, *last;
> -
> if ((offset_in_page(start)) || start > TASK_SIZE || len > TASK_SIZE-start)
> - return -EINVAL;
> + return false;
>
> - len = PAGE_ALIGN(len);
> - if (len == 0)
> - return -EINVAL;
> + if (PAGE_ALIGN(len) == 0)
> + return false;
> +
> + return true;
> +}
> +
> +/*
> + * munmap_lookup_vma: find the first overlap vma and split overlap vmas.
> + * @mm: mm_struct
> + * @vma: the first overlapping vma
> + * @prev: vma's prev
> + * @start: start address
> + * @end: end address
> + *
> + * returns 1 if successful, 0 or errno otherwise
> + */
> +static int munmap_lookup_vma(struct mm_struct *mm, struct vm_area_struct **vma,
> + struct vm_area_struct **prev, unsigned long start,
> + unsigned long end)
> +{
> + struct vm_area_struct *tmp, *last;
>
> /* Find the first overlapping VMA */
> - vma = find_vma(mm, start);
> - if (!vma)
> + tmp = find_vma(mm, start);
> + if (!tmp)
> return 0;
> - prev = vma->vm_prev;
> - /* we have start < vma->vm_end */
> +
> + *prev = tmp->vm_prev;
> +
> + /* we have start < vma->vm_end */
>
> /* if it doesn't overlap, we have nothing.. */
> - end = start + len;
> - if (vma->vm_start >= end)
> + if (tmp->vm_start >= end)
> return 0;
>
> /*
> @@ -2723,7 +2733,7 @@ int do_munmap(struct mm_struct *mm, unsigned long start, size_t len,
> * unmapped vm_area_struct will remain in use: so lower split_vma
> * places tmp vma above, and higher split_vma places tmp vma below.
> */
> - if (start > vma->vm_start) {
> + if (start > tmp->vm_start) {
> int error;
>
> /*
> @@ -2731,13 +2741,14 @@ int do_munmap(struct mm_struct *mm, unsigned long start, size_t len,
> * not exceed its limit; but let map_count go just above
> * its limit temporarily, to help free resources as expected.
> */
> - if (end < vma->vm_end && mm->map_count >= sysctl_max_map_count)
> + if (end < tmp->vm_end &&
> + mm->map_count > sysctl_max_map_count)
> return -ENOMEM;
>
> - error = __split_vma(mm, vma, start, 0);
> + error = __split_vma(mm, tmp, start, 0);
> if (error)
> return error;
> - prev = vma;
> + *prev = tmp;
> }
>
> /* Does it split the last one? */
> @@ -2747,7 +2758,48 @@ int do_munmap(struct mm_struct *mm, unsigned long start, size_t len,
> if (error)
> return error;
> }
> - vma = prev ? prev->vm_next : mm->mmap;
> +
> + *vma = *prev ? (*prev)->vm_next : mm->mmap;
> +
> + return 1;
> +}
> +
> +static inline void munmap_mlock_vma(struct vm_area_struct *vma,
> + unsigned long end)
> +{
> + struct vm_area_struct *tmp = vma;
> +
> + while (tmp && tmp->vm_start < end) {
> + if (tmp->vm_flags & VM_LOCKED) {
> + vma->vm_mm->locked_vm -= vma_pages(tmp);
> + munlock_vma_pages_all(tmp);
> + }
> + tmp = tmp->vm_next;
> + }
> +}
> +
> +/* Munmap is split into 2 main parts -- this part which finds
> + * what needs doing, and the areas themselves, which do the
> + * work. This now handles partial unmappings.
> + * Jeremy Fitzhardinge <jeremy@...p.org>
> + */
> +int do_munmap(struct mm_struct *mm, unsigned long start, size_t len,
> + struct list_head *uf)
> +{
> + unsigned long end;
> + struct vm_area_struct *vma = NULL, *prev;
> + int ret = 0;
> +
> + if (!munmap_addr_sanity(start, len))
> + return -EINVAL;
> +
> + len = PAGE_ALIGN(len);
> +
> + end = start + len;
> +
> + ret = munmap_lookup_vma(mm, &vma, &prev, start, end);
> + if (ret != 1)
> + return ret;
>
> if (unlikely(uf)) {
> /*
> @@ -2759,24 +2811,16 @@ int do_munmap(struct mm_struct *mm, unsigned long start, size_t len,
> * split, despite we could. This is unlikely enough
> * failure that it's not worth optimizing it for.
> */
> - int error = userfaultfd_unmap_prep(vma, start, end, uf);
> - if (error)
> - return error;
> + ret = userfaultfd_unmap_prep(vma, start, end, uf);
> + if (ret)
> + return ret;
> }
>
> /*
> * unlock any mlock()ed ranges before detaching vmas
> */
> - if (mm->locked_vm) {
> - struct vm_area_struct *tmp = vma;
> - while (tmp && tmp->vm_start < end) {
> - if (tmp->vm_flags & VM_LOCKED) {
> - mm->locked_vm -= vma_pages(tmp);
> - munlock_vma_pages_all(tmp);
> - }
> - tmp = tmp->vm_next;
> - }
> - }
> + if (mm->locked_vm)
> + munmap_mlock_vma(vma, end);
>
> /*
> * Remove the vma's, and unmap the actual pages
>
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