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

[ZhenweiPi]

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@xxxxxxxxx>
> > ---
> >   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