Re: [GIT PULL] Memory folios for v5.15

[Matthew Wilcox <willy@infradead.org>]

On Tue, Aug 24, 2021 at 03:44:48PM -0400, Theodore Ts'o wrote:
> On Tue, Aug 24, 2021 at 08:23:15PM +0100, Matthew Wilcox wrote:
> > > So when you mention "slab" as a name example, that's not the argument
> > > you think it is. That's a real honest-to-goodness operating system
> > > convention name that doesn't exactly predate Linux, but is most
> > > certainly not new.
> > 
> > Sure, but at the time Jeff Bonwick chose it, it had no meaning in
> > computer science or operating system design.
> 
> I think the big difference is that "slab" is mostly used as an
> internal name.  In Linux it doesn't even leak out to the users, since
> we use kmem_cache_{create,alloc,free,destroy}().  So the "slab"
> doesn't even show up in the API.

/proc/slabinfo
/proc/sys/vm/min_slab_ratio
/sys/kernel/slab
include/linux/slab.h
cpuset.memory_spread_slab
failslab=
slab_merge
slab_max_order=

$ git grep slab fs/ext4 |wc -l
30
(13 of which are slab.h)

> The problem is whether we use struct head_page, or folio, or mempages,
> we're going to be subsystem users' faces.  And people who are using it
> every day will eventually get used to anything, whether it's "folio"
> or "xmoqax", we sould give a thought to newcomers to Linux file system
> code.  If they see things like "read_folio()", they are going to be
> far more confused than "read_pages()" or "read_mempages()".
> 
> Sure, one impenetrable code word isn't that bad.  But this is a case
> of a death by a thousand cuts.  At $WORK, one time we had welcomed an
> intern to our group, I had to stop everyone each time that they used
> an acronym, or a codeword, and asked them to define the term.
> 
> It was really illuminating what an insider takes for granted, but when
> it's one cutsy codeword after another, with three or more such
> codewords in a sentence, it's *really* a less-than-great initial
> experience for a newcomer.
> 
> So if someone sees "kmem_cache_alloc()", they can probably make a
> guess what it means, and it's memorable once they learn it.
> Similarly, something like "head_page", or "mempages" is going to a bit
> more obvious to a kernel newbie.  So if we can make a tiny gesture
> towards comprehensibility, it would be good to do so while it's still
> easier to change the name.

I completely agree that it's good to use something which is not jargon,
or is at least widely-understood jargon.  And I loathe acronyms (you'll
notice I haven't suggested a single one).  Folio/ream/quire/sheaf were
all attempts to get across "collection of pages".  Another direction
would be something that is associated with memory (but I don't have
a good example).  Or a non-English word (roman?  seite?  sidor?)

We're going to end up with hpage, aren't we?