Re: [patch 4/4] dm-writecache: use new API for flushing

From: Mikulas Patocka <mpatocka@redhat.com>
To: Mike Snitzer <snitzer@redhat.com>
Cc: device-mapper development <dm-devel@redhat.com>,
	linux-nvdimm <linux-nvdimm@lists.01.org>
Subject: Re: [patch 4/4] dm-writecache: use new API for flushing
Date: Wed, 30 May 2018 10:09:02 -0400 (EDT)	[thread overview]
Message-ID: <alpine.LRH.2.02.1805300959460.16696@file01.intranet.prod.int.rdu2.redhat.com> (raw)
In-Reply-To: <20180530135421.GA81788@redhat.com>

On Wed, 30 May 2018, Mike Snitzer wrote:

> On Wed, May 30 2018 at  9:33am -0400,
> Mikulas Patocka <mpatocka@redhat.com> wrote:
> 
> > 
> > 
> > On Wed, 30 May 2018, Mike Snitzer wrote:
> > 
> > > On Wed, May 30 2018 at  9:21am -0400,
> > > Mikulas Patocka <mpatocka@redhat.com> wrote:
> > > 
> > > > 
> > > > 
> > > > On Wed, 30 May 2018, Mike Snitzer wrote:
> > > > 
> > > > > That is really great news, can you submit an incremental patch that
> > > > > layers ontop of the linux-dm.git 'dm-4.18' branch?
> > > > > 
> > > > > Thanks,
> > > > > Mike
> > > > 
> > > > I've sent the current version that I have. I fixed the bugs that were 
> > > > reported here (missing DAX, dm_bufio_client_create, __branch_check__ 
> > > > long->int truncation).
> > > 
> > > OK, but a monolithic dm-writecache.c is no longer useful to me.  I can
> > > drop Arnd's gcc warning fix (with the idea that Ingo or Steve will take
> > > your __branch_check__ patch).  Not sure what the dm_bufio_client_create
> > > fix is... must've missed a report about that.
> > > 
> > > ANyway, point is we're on too a different phase of dm-writecache.c's
> > > development.  I've picked it up and am trying to get it ready for the
> > > 4.18 merge window (likely opening Sunday).  Therefore it needs to be in
> > > a git tree, and incremental changes overlayed.  I cannot be rebasing at
> > > this late stage in the 4.18 development window.
> > > 
> > > Thanks,
> > > Mike
> > 
> > I downloaded dm-writecache from your git repository some times ago - but 
> > you changed a lot of useless things (i.e. reordering the fields in the 
> > structure) since that time - so, you'll have to merge the changes.
> 
> Fine I'll deal with it.  reordering the fields eliminated holes in the
> structure and reduced struct members spanning cache lines.

And what about this?
#define WC_MODE_PMEM(wc)                        ((wc)->pmem_mode)

The code that I had just allowed the compiler to optimize out 
persistent-memory code if we have DM_WRITECACHE_ONLY_SSD defined - and you 
deleted it.

Most architectures don't have persistent memory and the dm-writecache 
driver could work in ssd-only mode on them. On these architectures, I 
define
#define WC_MODE_PMEM(wc)                        false
- and the compiler will just automatically remove the tests for that 
condition and the unused branch. It does also eliminate unused static 
functions.

Mikulas
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