linux-kernel - Re: [PATCH v5 05/78] xarray: Replace exceptional entries

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Message-ID: <20171227030534.GA24828@bombadil.infradead.org>
Date:   Tue, 26 Dec 2017 19:05:34 -0800
From:   Matthew Wilcox <willy@...radead.org>
To:     "Kirill A. Shutemov" <kirill@...temov.name>
Cc:     linux-kernel@...r.kernel.org,
        Matthew Wilcox <mawilcox@...rosoft.com>,
        Ross Zwisler <ross.zwisler@...ux.intel.com>,
        David Howells <dhowells@...hat.com>,
        Shaohua Li <shli@...nel.org>, Jens Axboe <axboe@...nel.dk>,
        Rehas Sachdeva <aquannie@...il.com>,
        Marc Zyngier <marc.zyngier@....com>, linux-mm@...ck.org,
        linux-fsdevel@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net,
        linux-nilfs@...r.kernel.org, linux-btrfs@...r.kernel.org,
        linux-xfs@...r.kernel.org, linux-usb@...r.kernel.org,
        linux-raid@...r.kernel.org
Subject: Re: [PATCH v5 05/78] xarray: Replace exceptional entries

On Tue, Dec 26, 2017 at 08:15:42PM +0300, Kirill A. Shutemov wrote:
> >  28 files changed, 249 insertions(+), 240 deletions(-)
> 
> Everything looks fine to me after quick scan, but hat's a lot of changes for
> one patch...

Yeah.  It's pretty mechanical though.

> > -			if (radix_tree_exceptional_entry(page)) {
> > +			if (xa_is_value(page)) {
> >  				if (!invalidate_exceptional_entry2(mapping,
> >  								   index, page))
> >  					ret = -EBUSY;
> 
> invalidate_exceptional_entry? Are we going to leave the terminology here as is?

That is a great question.  If the page cache wants to call its value
entries exceptional entries, it can continue to do that.  I think there's
a better name for them, but I'm not sure what it is.  Right now, the
page cache uses value entries to store:

1. Shadow entries (for workingset)
2. Swap entries (for shmem)
3. DAX entries

I can't come up with a good name for these three things.  'nonpage' is
the only thing which hasn't immediately fallen off my ideas list.  But
I think renaming exceptional entries in the page cache is a great idea,
and I don't want to do it as part of this patch set ;-)