From: Yang Shi <yang.shi@linux.alibaba.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: mhocko@kernel.org, willy@infradead.org,
ldufour@linux.vnet.ibm.com, akpm@linux-foundation.org,
mingo@redhat.com, acme@kernel.org,
alexander.shishkin@linux.intel.com, jolsa@redhat.com,
namhyung@kernel.org, linux-mm@kvack.org,
linux-kernel@vger.kernel.org
Subject: Re: [RFC v2 PATCH 2/2] mm: mmap: zap pages with read mmap_sem for large mapping
Date: Tue, 19 Jun 2018 14:13:05 -0700 [thread overview]
Message-ID: <f78924fc-ea81-9ddd-ebb2-28241d5721c8@linux.alibaba.com> (raw)
In-Reply-To: <20180619100218.GN2458@hirez.programming.kicks-ass.net>
On 6/19/18 3:02 AM, Peter Zijlstra wrote:
> On Tue, Jun 19, 2018 at 07:34:16AM +0800, Yang Shi wrote:
>
>> diff --git a/mm/mmap.c b/mm/mmap.c
>> index fc41c05..e84f80c 100644
>> --- a/mm/mmap.c
>> +++ b/mm/mmap.c
>> @@ -2686,6 +2686,141 @@ int split_vma(struct mm_struct *mm, struct vm_area_struct *vma,
>> return __split_vma(mm, vma, addr, new_below);
>> }
>>
>> +/* Consider PUD size or 1GB mapping as large mapping */
>> +#ifdef HPAGE_PUD_SIZE
>> +#define LARGE_MAP_THRESH HPAGE_PUD_SIZE
>> +#else
>> +#define LARGE_MAP_THRESH (1 * 1024 * 1024 * 1024)
>> +#endif
>> +
>> +/* Unmap large mapping early with acquiring read mmap_sem */
>> +static int do_munmap_zap_early(struct mm_struct *mm, unsigned long start,
>> + size_t len, struct list_head *uf)
>> +{
>> + unsigned long end = 0;
>> + struct vm_area_struct *vma = NULL, *prev, *last, *tmp;
>> + bool success = false;
>> + int ret = 0;
>> +
>> + if ((offset_in_page(start)) || start > TASK_SIZE || len > TASK_SIZE - start)
>> + return -EINVAL;
>> +
>> + len = (PAGE_ALIGN(len));
>> + if (len == 0)
>> + return -EINVAL;
>> +
>> + /* Just deal with uf in regular path */
>> + if (unlikely(uf))
>> + goto regular_path;
>> +
>> + if (len >= LARGE_MAP_THRESH) {
>> + down_read(&mm->mmap_sem);
>> + vma = find_vma(mm, start);
>> + if (!vma) {
>> + up_read(&mm->mmap_sem);
>> + return 0;
>> + }
>> +
>> + prev = vma->vm_prev;
>> +
>> + end = start + len;
>> + if (vma->vm_start > end) {
>> + up_read(&mm->mmap_sem);
>> + return 0;
>> + }
>> +
>> + if (start > vma->vm_start) {
>> + int error;
>> +
>> + if (end < vma->vm_end &&
>> + mm->map_count > sysctl_max_map_count) {
>> + up_read(&mm->mmap_sem);
>> + return -ENOMEM;
>> + }
>> +
>> + error = __split_vma(mm, vma, start, 0);
>> + if (error) {
>> + up_read(&mm->mmap_sem);
>> + return error;
>> + }
>> + prev = vma;
>> + }
>> +
>> + last = find_vma(mm, end);
>> + if (last && end > last->vm_start) {
>> + int error = __split_vma(mm, last, end, 1);
>> +
>> + if (error) {
>> + up_read(&mm->mmap_sem);
>> + return error;
>> + }
>> + }
>> + vma = prev ? prev->vm_next : mm->mmap;
> Hold up, two things: you having to copy most of do_munmap() didn't seem
> to suggest a helper function? And second, since when are we allowed to
Yes, they will be extracted into a helper function in the next version.
May bad, I don't think it is allowed. We could reform this to:
acquire write mmap_sem
vma lookup (split vmas)
release write mmap_sem
acquire read mmap_sem
zap pages
release read mmap_sem
I'm supposed this is safe as what Michal said before.
Thanks,
Yang
> split VMAs under a read lock?
next prev parent reply other threads:[~2018-06-19 21:13 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-06-18 23:34 [RFC v2 0/2] mm: zap pages with read mmap_sem in munmap for large mapping Yang Shi
2018-06-18 23:34 ` [RFC v2 PATCH 1/2] uprobes: make vma_has_uprobes non-static Yang Shi
2018-06-18 23:34 ` [RFC v2 PATCH 2/2] mm: mmap: zap pages with read mmap_sem for large mapping Yang Shi
2018-06-19 10:02 ` Peter Zijlstra
2018-06-19 21:13 ` Yang Shi [this message]
2018-06-20 7:17 ` Michal Hocko
2018-06-20 16:23 ` Yang Shi
2018-06-19 22:17 ` Nadav Amit
[not found] ` <158a4e4c-d290-77c4-a595-71332ede392b@linux.alibaba.com>
2018-06-20 0:31 ` Nadav Amit
2018-06-20 7:18 ` Michal Hocko
2018-06-20 17:12 ` Nadav Amit
2018-06-20 18:42 ` Yang Shi
2018-06-23 1:01 ` Yang Shi
2018-06-25 9:14 ` Michal Hocko
2018-06-26 0:06 ` Yang Shi
2018-06-26 7:43 ` Peter Zijlstra
2018-06-27 1:03 ` Yang Shi
2018-06-27 7:24 ` Michal Hocko
2018-06-27 17:23 ` Yang Shi
2018-06-28 11:51 ` Michal Hocko
2018-06-28 19:10 ` Yang Shi
2018-06-29 0:59 ` Yang Shi
2018-06-29 11:39 ` Michal Hocko
2018-06-29 16:50 ` Yang Shi
2018-06-29 11:34 ` Michal Hocko
2018-06-29 16:45 ` Yang Shi
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