Re: xdr nfs highmem deadlock fix [Re: filesystem access slowing system to a crawl]

[Andrew Morton <akpm@digeo.com>]

Trond Myklebust <trond.myklebust@fys.uio.no> wrote:
>
> >>>>> " " == Andrea Arcangeli <andrea@suse.de> writes:
> 
>      > 2.5.62 has the very same deadlock condition in xdr triggered by
>      >        nfs too.
>      > Andrew, if you're forward porting it yourself like with the
>      > filebacked vma merging feature just let me know so we make sure
>      > not to duplicate effort.
> 
> For 2.5.x we should rather fix MSG_MORE so that it actually works
> instead of messing with hacks to kmap().

Is the fixing of MSG_MORE likely to actually happen?

> For 2.4.x, Hirokazu Takahashi had a patch which allowed for a safe
> kmap of > 1 page in one call. Appended here as an attachment FYI
> (Marcelo do *not* apply!).

Andrea's patch is quite simple.  Although I wonder if this, in
xdr_kmap():

+		} else {
+			iov->iov_base = kmap_nonblock(*ppage);
+			if (!iov->iov_base)
+				goto out;
+		}

should be skipping the map_tail thing?