linux-kernel - Re: [PATCH v2] mm/vmalloc: terminate searching since one node found

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Message-ID: <596C7D99.5040208@zoho.com>
Date:   Mon, 17 Jul 2017 17:04:25 +0800
From:   zijun_hu <zijun_hu@...o.com>
To:     Zhaoyang Huang <huangzhaoyang@...il.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org, zijun_hu@....com
Subject: Re: [PATCH v2] mm/vmalloc: terminate searching since one node found

On 07/17/2017 04:45 PM, zijun_hu wrote:
> On 07/17/2017 04:07 PM, Zhaoyang Huang wrote:
>> It is no need to find the very beginning of the area within
>> alloc_vmap_area, which can be done by judging each node during the process
>>
>> For current approach, the worst case is that the starting node which be found
>> for searching the 'vmap_area_list' is close to the 'vstart', while the final
>> available one is round to the tail(especially for the left branch).
>> This commit have the list searching start at the first available node, which
>> will save the time of walking the rb tree'(1)' and walking the list(2).
>>
>>       vmap_area_root
>>           /      \
>>      tmp_next     U
>>         /   (1)
>>       tmp
>>        /
>>      ...
>>       /
>>     first(current approach)
>>
>> vmap_area_list->...->first->...->tmp->tmp_next
> 
> the original code can ensure the following two points :
> A, the result vamp_area has the lowest available address in the range [vstart, vend)
> B, it can maintain the cached vamp_area node rightly which can speedup relative allocation
> i suspect this patch maybe destroy the above two points 
>>                             (2)
>>
>> Signed-off-by: Zhaoyang Huang <zhaoyang.huang@...eadtrum.com>
>> ---
>>  mm/vmalloc.c | 7 +++++++
>>  1 file changed, 7 insertions(+)
>>
>> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
>> index 34a1c3e..f833e07 100644
>> --- a/mm/vmalloc.c
>> +++ b/mm/vmalloc.c
>> @@ -459,9 +459,16 @@ static struct vmap_area *alloc_vmap_area(unsigned
>> long size,
>>
>>                 while (n) {
>>                         struct vmap_area *tmp;
>> +                       struct vmap_area *tmp_next;
>>                         tmp = rb_entry(n, struct vmap_area, rb_node);
>> +                       tmp_next = list_next_entry(tmp, list);
>>                         if (tmp->va_end >= addr) {
>>                                 first = tmp;
>> +                               if (ALIGN(tmp->va_end, align) + size
>> +                                               < tmp_next->va_start) {
>> +                                       addr = ALIGN(tmp->va_end, align);
>> +                                       goto found;
>> +                               }
> is the aim vamp_area the lowest available one if the goto occurs ?
> it will bypass the latter cached vamp_area info  cached_hole_size update possibly if the goto occurs
  it think the aim area maybe don't locates the required range [vstart, vend) possibly.
>>                                 if (tmp->va_start <= addr)
>>                                         break;
>>                                 n = n->rb_left;
>> --
>> 1.9.1
>>
>