linux-kernel - Re: [PATCH 6/7] mm: Pass pvec directly to find_get

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Message-ID: <20200825123324.GB32298@quack2.suse.cz>
Date:   Tue, 25 Aug 2020 14:33:24 +0200
From:   Jan Kara <jack@...e.cz>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Jan Kara <jack@...e.cz>, linux-mm@...ck.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Hugh Dickins <hughd@...gle.com>,
        William Kucharski <william.kucharski@...cle.com>,
        Johannes Weiner <hannes@...xchg.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 6/7] mm: Pass pvec directly to find_get_entries

On Mon 24-08-20 18:36:39, Matthew Wilcox wrote:
> On Mon, Aug 24, 2020 at 06:16:20PM +0200, Jan Kara wrote:
> > On Wed 19-08-20 16:05:54, Matthew Wilcox (Oracle) wrote:
> > > All callers of find_get_entries() use a pvec, so pass it directly
> > > instead of manipulating it in the caller.
> > > 
> > > Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
> > 
> > Rather than passing pvec to find_get_entries() and then making everybody
> > use it, won't it more consistent WRT the naming to make everybody use
> > pagevec_lookup_entries() (which is trivial at this point in the series) and
> > then rename find_get_entries() to pagevec_lookup_entries()? I.e., I'd prefer
> > if the final function was called pagevec_lookup_entries() because that is
> > IMO more consistent with how other functions are named in this area...
> 
> It seemed more consistent to me to have everybody using
> find_get_entries().  To me the pagevec functions:
> 
> 1. Are in mm/swap.c (not really sure why)

Historical :). AFAIK pagevec abstraction was first created to make swapping
out and reclaim of pages more effective. It has grown a bit since then...

> 2. Take pvec as the first argument, not the last

Well, yes, I'd keep the argument order to match original
pagevec_lookup_entries().

> 3. Wrap a find_* function
> 
> Whereas the find_* functions:
> 
> 1. Are in mm/filemap.c
> 2. Take mapping as the first argument
> 3. Manipulate the XArray directly

Agreed.

> We already have functions in filemap which take a pagevec, eg
> page_cache_delete_batch() and delete_from_page_cache_batch().

Right but those are really pretty internal helper functions so I don't
think they form or strong precedence.

> So if we're going to merge the two functions, it seems more natural to
> have it in filemap.c and called find_get_entries(), but I'm definitely
> open to persuasion on this!

I agree that having non-trivial xarray code in mm/swap.c isn't attractive
either. Dunno, I dislike the inconsistency between find_get_pages() and
find_get_entries() you create but they aren't completely consistent anyway
so I can live with that. Or we can just leave the pagevec_lookup_entries()
wrapper and the API will stay consistent...

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR