linux-kernel - Re: [PATCH] mm: don't zero ballooned pages

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Date:   Mon, 31 Jul 2017 15:39:35 +0800
From:   ZhenweiPi <zhenwei.pi@...runcloud.com>
To:     Michal Hocko <mhocko@...nel.org>, Wei Wang <wei.w.wang@...el.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        virtualization@...ts.linux-foundation.org, mst@...hat.com,
        mawilcox@...rosoft.com, dave.hansen@...el.com,
        akpm@...ux-foundation.org
Subject: Re: [PATCH] mm: don't zero ballooned pages

on qemu upstream, code in qemu/util/osdep.c

int qemu_madvise(void *addr, size_t len, int advice)

{

     if (advice == QEMU_MADV_INVALID) {

         errno = EINVAL;

         return -1;

     }

#if defined(CONFIG_MADVISE)

     return madvise(addr, len, advice);

#elif defined(CONFIG_POSIX_MADVISE)

     return posix_madvise(addr, len, advice);

#else

     errno = EINVAL;

     return -1;

#endif

}

Host OS maybe not support MADV_DONTNEED.
And madvise syscall uses more time.


On 07/31/2017 02:55 PM, Michal Hocko wrote:
> On Mon 31-07-17 12:13:33, Wei Wang wrote:
>> Ballooned pages will be marked as MADV_DONTNEED by the hypervisor and
>> shouldn't be given to the host ksmd to scan.
> Could you point me where this MADV_DONTNEED is done, please?
>
>> Therefore, it is not
>> necessary to zero ballooned pages, which is very time consuming when
>> the page amount is large. The ongoing fast balloon tests show that the
>> time to balloon 7G pages is increased from ~491ms to 2.8 seconds with
>> __GFP_ZERO added. So, this patch removes the flag.
> Please make it obvious that this is a revert of bb01b64cfab7
> ("mm/balloon_compaction.c: enqueue zero page to balloon device").
>
>> Signed-off-by: Wei Wang <wei.w.wang@...el.com>
>> ---
>>   mm/balloon_compaction.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/mm/balloon_compaction.c b/mm/balloon_compaction.c
>> index 9075aa5..b06d9fe 100644
>> --- a/mm/balloon_compaction.c
>> +++ b/mm/balloon_compaction.c
>> @@ -24,7 +24,7 @@ struct page *balloon_page_enqueue(struct balloon_dev_info *b_dev_info)
>>   {
>>   	unsigned long flags;
>>   	struct page *page = alloc_page(balloon_mapping_gfp_mask() |
>> -				__GFP_NOMEMALLOC | __GFP_NORETRY | __GFP_ZERO);
>> +				       __GFP_NOMEMALLOC | __GFP_NORETRY);
>>   	if (!page)
>>   		return NULL;
>>   
>> -- 
>> 2.7.4
>>