linux-kernel - Re: [PATCH 09/12] xfs: refactor the ioend merging code

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Date:   Tue, 25 Jun 2019 12:14:45 +0200
From:   Christoph Hellwig <hch@....de>
To:     Nikolay Borisov <nborisov@...e.com>
Cc:     Christoph Hellwig <hch@....de>,
        "Darrick J . Wong" <darrick.wong@...cle.com>,
        Damien Le Moal <Damien.LeMoal@....com>,
        Andreas Gruenbacher <agruenba@...hat.com>,
        linux-xfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 09/12] xfs: refactor the ioend merging code

On Mon, Jun 24, 2019 at 07:06:22PM +0300, Nikolay Borisov wrote:
> > +{
> > +	struct list_head	tmp;
> > +
> > +	list_replace_init(&ioend->io_list, &tmp);
> > +	xfs_destroy_ioend(ioend, error);
> > +	while ((ioend = list_pop(&tmp, struct xfs_ioend, io_list)))
> > +		xfs_destroy_ioend(ioend, error);
> 
> nit: I'd prefer if the list_pop patch is right before this one since
> this is the first user of it.

I try to keep generic infrastructure first instead of interveawing
it with subystem-specific patches.

> Additionally, I don't think list_pop is
> really a net-negative win 

What is a "net-negative win" ?

> in comparison to list_for_each_entry_safe
> here. In fact this "delete the list" would seems more idiomatic if
> implemented via list_for_each_entry_safe

I disagree.  The for_each loops require an additional next iterator,
and also don't clearly express what is going on, but require additional
spotting of the list_del.