Re: [RFC PATCH 1/2] mm: swap: check if swap backing device is congested or not

[Yang Shi]

On 12/18/18 4:16 PM, Tim Chen wrote:
> On 12/18/18 3:43 PM, Yang Shi wrote:
> > On 12/18/18 11:29 AM, Tim Chen wrote:
> > > On 12/17/18 10:52 PM, Yang Shi wrote:
> > >
> > > > diff --git a/mm/swap_state.c b/mm/swap_state.c
> > > > index fd2f21e..7cc3c29 100644
> > > > --- a/mm/swap_state.c
> > > > +++ b/mm/swap_state.c
> > > > @@ -538,11 +538,15 @@ struct page *swap_cluster_readahead(swp_entry_t entry, gfp_t gfp_mask,
> > > >  ÂÂÂÂÂ bool do_poll = true, page_allocated;
> > > >  ÂÂÂÂÂ struct vm_area_struct *vma = vmf->vma;
> > > >  ÂÂÂÂÂ unsigned long addr = vmf->address;
> > > > +ÂÂÂ struct inode *inode = si->swap_file->f_mapping->host;
> > > >  Â ÂÂÂÂÂ mask = swapin_nr_pages(offset) - 1;
> > > >  ÂÂÂÂÂ if (!mask)
> > > >  ÂÂÂÂÂÂÂÂÂ goto skip;
> > > >    
> > > Shmem will also be using this function and I don't think the inode_read_congested
> > > logic is relevant for that case.
> > IMHO, shmem is also relevant. As long as it is trying to readahead from swap, it should check if the underlying device is busy or not regardless of shmem or anon page.
> I don't think your dereference inode = si->swap_file->f_mapping->host
> is always safe.  You should do it only when (si->flags & SWP_FS) is true.

Do you mean it is not safe for swap partition?

I tested with swap partition too. It looks fine. Opening block device 
also gets inode.

FilenameÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ TypeÂÂÂÂÂÂÂÂÂÂÂ Size UsedÂÂÂ 
Priority
/dev/sdb1ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ partition 20970492ÂÂÂÂÂÂÂ 850168Â -2

Thanks,
Yang

> Tim