lkml.org 
[lkml]   [2020]   [Aug]   [24]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 0/5] bio: Direct IO: convert to pin_user_pages_fast()
On Tue, Aug 25, 2020 at 02:54:28AM +0100, Al Viro wrote:
> On Fri, Aug 21, 2020 at 09:20:54PM -0700, John Hubbard wrote:
>
> > Direct IO behavior:
> >
> > ITER_IOVEC:
> > pin_user_pages_fast();
> > break;
> >
> > ITER_KVEC: // already elevated page refcount, leave alone
> > ITER_BVEC: // already elevated page refcount, leave alone
> > ITER_PIPE: // just, no :)
>
> Why? What's wrong with splice to O_DIRECT file?

Sorry - s/to/from/, obviously.

To spell it out: consider generic_file_splice_read() behaviour when
the source had been opened with O_DIRECT; you will get a call of
->read_iter() into ITER_PIPE destination. And it bloody well
will hit iov_iter_get_pages() on common filesystems, to pick the
pages we want to read into.

So... what's wrong with having that "pin" primitive making sure
the pages are there and referenced by the pipe?

\
 
 \ /
  Last update: 2020-08-25 04:07    [W:0.194 / U:0.020 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site