Re: [PATCH v2: [linux-4.14.y] ] dm cache: submit writethrough writes in parallel to origin and cache

[John Donnelly]

On 7/31/20 1:54 AM, Greg KH wrote:
> On Thu, Jul 30, 2020 at 03:33:42PM -0500, John Donnelly wrote:
> > From: Mike Snitzer <snitzer@xxxxxxxxxx>
> >
> > Discontinue issuing writethrough write IO in series to the origin and
> > then cache.
> >
> > Use bio_clone_fast() to create a new origin clone bio that will be
> > mapped to the origin device and then bio_chain() it to the bio that gets
> > remapped to the cache device.  The origin clone bio does _not_ have a
> > copy of the per_bio_data -- as such check_if_tick_bio_needed() will not
> > be called.
> >
> > The cache bio (parent bio) will not complete until the origin bio has
> > completed -- this fulfills bio_clone_fast()'s requirements as well as
> > the requirement to not complete the original IO until the write IO has
> > completed to both the origin and cache device.
> >
> > Signed-off-by: Mike Snitzer <snitzer@xxxxxxxxxx>
> >
> > (cherry picked from commit 2df3bae9a6543e90042291707b8db0cbfbae9ee9)
> >
> > Fixes: 4ec34f2196d125ff781170ddc6c3058c08ec5e73 (dm bio record:
> > save/restore bi_end_io and bi_integrity )
> >
> > 4ec34f21 introduced a mkfs.ext4 hang on a LVM device that has been
> > modified with lvconvert --cachemode=writethrough.
> >
> > CC:stable@xxxxxxxxxxxxxxx for 4.14.x .
> >
> > Signed-off-by: John Donnelly <john.p.donnelly@xxxxxxxxxx>
> > Reviewed-by: Somasundaram Krishnasamy <somasundaram.krishnasamy@xxxxxxxxxx>
> >
> > conflicts:
> > 	drivers/md/dm-cache-target.c. -  Corrected usage of
> > 	writethrough_mode(&cache->feature) that was caught by
> > 	compiler, and removed unused static functions : writethrough_endio(),
> > 	defer_writethrough_bio(), wake_deferred_writethrough_worker()
> > 	that generated warnings.
> > ---
> >   drivers/md/dm-cache-target.c | 94
> > ++++++++++++++++++--------------------------
>
> Line wrapped?

 ummm .. that is weird

> >   1 file changed, 38 insertions(+), 56 deletions(-)
> >
> > diff --git a/drivers/md/dm-cache-target.c b/drivers/md/dm-cache-target.c
> > index 69cdb29ef6be..2d9566bfe08b 100644
> > --- a/drivers/md/dm-cache-target.c
> > +++ b/drivers/md/dm-cache-target.c
> > @@ -1,5 +1,5 @@
> >   /*
> > - * Copyright (C) 2012 Red Hat. All rights reserved.
> > + i Copyright (C) 2012 Red Hat. All rights reserved.
>
> What happened here?

 spurious character from vi ;-(

> This patch can't be applied as-is :(
>
> greg k-h

 I will repost next week Thank you.