linux-kernel - Re: [PATCH RFC 1/3] mm/gup: consistently name GUP-fast functions

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Date: Wed, 27 Mar 2024 10:52:56 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: David Hildenbrand <david@...hat.com>
Cc: linux-kernel@...r.kernel.org, Andrew Morton <akpm@...ux-foundation.org>,
	Mike Rapoport <rppt@...nel.org>, John Hubbard <jhubbard@...dia.com>,
	Peter Xu <peterx@...hat.com>, linux-arm-kernel@...ts.infradead.org,
	loongarch@...ts.linux.dev, linux-mips@...r.kernel.org,
	linuxppc-dev@...ts.ozlabs.org, linux-s390@...r.kernel.org,
	linux-sh@...r.kernel.org, linux-mm@...ck.org,
	linux-perf-users@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	x86@...nel.org
Subject: Re: [PATCH RFC 1/3] mm/gup: consistently name GUP-fast functions

On Wed, Mar 27, 2024 at 02:05:36PM +0100, David Hildenbrand wrote:
> Let's consistently call the "fast-only" part of GUP "GUP-fast" and rename
> all relevant internal functions to start with "gup_fast", to make it
> clearer that this is not ordinary GUP. The current mixture of
> "lockless", "gup" and "gup_fast" is confusing.
> 
> Further, avoid the term "huge" when talking about a "leaf" -- for
> example, we nowadays check pmd_leaf() because pmd_huge() is gone. For the
> "hugepd"/"hugepte" stuff, it's part of the name ("is_hugepd"), so that
> says.
> 
> What remains is the "external" interface:
> * get_user_pages_fast_only()
> * get_user_pages_fast()
> * pin_user_pages_fast()
> 
> And the "internal" interface that handles GUP-fast + fallback:
> * internal_get_user_pages_fast()

This would like a better name too. How about gup_fast_fallback() ?

> The high-level internal function for GUP-fast is now:
> * gup_fast()
> 
> The basic GUP-fast walker functions:
> * gup_pgd_range() -> gup_fast_pgd_range()
> * gup_p4d_range() -> gup_fast_p4d_range()
> * gup_pud_range() -> gup_fast_pud_range()
> * gup_pmd_range() -> gup_fast_pmd_range()
> * gup_pte_range() -> gup_fast_pte_range()
> * gup_huge_pgd()  -> gup_fast_pgd_leaf()
> * gup_huge_pud()  -> gup_fast_pud_leaf()
> * gup_huge_pmd()  -> gup_fast_pmd_leaf()
> 
> The weird hugepd stuff:
> * gup_huge_pd() -> gup_fast_hugepd()
> * gup_hugepte() -> gup_fast_hugepte()
> 
> The weird devmap stuff:
> * __gup_device_huge_pud() -> gup_fast_devmap_pud_leaf()
> * __gup_device_huge_pmd   -> gup_fast_devmap_pmd_leaf()
> * __gup_device_huge()     -> gup_fast_devmap_leaf()
>
> Helper functions:
> * unpin_user_pages_lockless() -> gup_fast_unpin_user_pages()
> * gup_fast_folio_allowed() is already properly named
> * gup_fast_permitted() is already properly named
> 
> With "gup_fast()", we now even have a function that is referred to in
> comment in mm/mmu_gather.c.
> 
> Signed-off-by: David Hildenbrand <david@...hat.com>
> ---
>  mm/gup.c | 164 ++++++++++++++++++++++++++++---------------------------
>  1 file changed, 84 insertions(+), 80 deletions(-)

I think it is a great idea, it always takes a moment to figure out if
a function is part of the fast callchain or not..

(even better would be to shift the fast stuff into its own file, but I
expect that is too much)

Reviewed-by: Jason Gunthorpe <jgg@...dia.com>

Jason