Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1406281

Re: [PATCH RESEND 7/8] pipe: account to kmemcg

Show all headers | View raw

On Tue, May 24, 2016 at 05:59:02AM -0700, Eric Dumazet wrote:
...
> > +static int anon_pipe_buf_steal(struct pipe_inode_info *pipe,
> > +			       struct pipe_buffer *buf)
> > +{
> > +	struct page *page = buf->page;
> > +
> > +	if (page_count(page) == 1) {
> 
> This looks racy : some cpu could have temporarily elevated page count.

All pipe operations (pipe_buf_operations->get, ->release, ->steal) are
supposed to be called under pipe_lock. So, if we see a pipe_buffer->page
with refcount of 1 in ->steal, that means that we are the only its user
and it can't be spliced to another pipe.

In fact, I just copied the code from generic_pipe_buf_steal, adding
kmemcg related checks along the way, so it should be fine.

Thanks,
Vladimir

> 
> > +		if (memcg_kmem_enabled()) {
> > +			memcg_kmem_uncharge(page, 0);
> > +			__ClearPageKmemcg(page);
> > +		}
> > +		__SetPageLocked(page);
> > +		return 0;
> > +	}
> > +	return 1;
> > +}

Back to linux.kernel | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

[PATCH RESEND 7/8] pipe: account to kmemcg Vladimir Davydov <vdavydov@virtuozzo.com> - 2016-05-24 11:10 +0200
  Re: [PATCH RESEND 7/8] pipe: account to kmemcg Eric Dumazet <eric.dumazet@gmail.com> - 2016-05-24 15:00 +0200
    Re: [PATCH RESEND 7/8] pipe: account to kmemcg Vladimir Davydov <vdavydov@virtuozzo.com> - 2016-05-24 18:50 +0200
      Re: [PATCH RESEND 7/8] pipe: account to kmemcg Eric Dumazet <eric.dumazet@gmail.com> - 2016-05-24 22:10 +0200
        Re: [PATCH RESEND 7/8] pipe: account to kmemcg Vladimir Davydov <vdavydov@virtuozzo.com> - 2016-05-25 12:40 +0200
          Re: [PATCH RESEND 7/8] pipe: account to kmemcg Minchan Kim <minchan@kernel.org> - 2016-05-26 09:10 +0200
            Re: [PATCH RESEND 7/8] pipe: account to kmemcg Vladimir Davydov <vdavydov@virtuozzo.com> - 2016-05-26 16:00 +0200
              Re: [PATCH RESEND 7/8] pipe: account to kmemcg Eric Dumazet <eric.dumazet@gmail.com> - 2016-05-26 16:20 +0200

csiph-web