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Date: Wed, 18 Dec 2019 16:32:28 -0800 From: John Hubbard <jhubbard@...dia.com> To: "Kirill A. Shutemov" <kirill@...temov.name> CC: Andrew Morton <akpm@...ux-foundation.org>, Al Viro <viro@...iv.linux.org.uk>, Alex Williamson <alex.williamson@...hat.com>, Benjamin Herrenschmidt <benh@...nel.crashing.org>, Björn Töpel <bjorn.topel@...el.com>, Christoph Hellwig <hch@...radead.org>, Dan Williams <dan.j.williams@...el.com>, Daniel Vetter <daniel@...ll.ch>, Dave Chinner <david@...morbit.com>, David Airlie <airlied@...ux.ie>, "David S . Miller" <davem@...emloft.net>, Ira Weiny <ira.weiny@...el.com>, Jan Kara <jack@...e.cz>, Jason Gunthorpe <jgg@...pe.ca>, Jens Axboe <axboe@...nel.dk>, Jonathan Corbet <corbet@....net>, Jérôme Glisse <jglisse@...hat.com>, Magnus Karlsson <magnus.karlsson@...el.com>, Mauro Carvalho Chehab <mchehab@...nel.org>, Michael Ellerman <mpe@...erman.id.au>, Michal Hocko <mhocko@...e.com>, Mike Kravetz <mike.kravetz@...cle.com>, Paul Mackerras <paulus@...ba.org>, Shuah Khan <shuah@...nel.org>, Vlastimil Babka <vbabka@...e.cz>, <bpf@...r.kernel.org>, <dri-devel@...ts.freedesktop.org>, <kvm@...r.kernel.org>, <linux-block@...r.kernel.org>, <linux-doc@...r.kernel.org>, <linux-fsdevel@...r.kernel.org>, <linux-kselftest@...r.kernel.org>, <linux-media@...r.kernel.org>, <linux-rdma@...r.kernel.org>, <linuxppc-dev@...ts.ozlabs.org>, <netdev@...r.kernel.org>, <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org>, Christoph Hellwig <hch@....de> Subject: Re: [PATCH v11 04/25] mm: devmap: refactor 1-based refcounting for ZONE_DEVICE pages On 12/18/19 8:04 AM, Kirill A. Shutemov wrote: > On Mon, Dec 16, 2019 at 02:25:16PM -0800, John Hubbard wrote: >> An upcoming patch changes and complicates the refcounting and >> especially the "put page" aspects of it. In order to keep >> everything clean, refactor the devmap page release routines: >> >> * Rename put_devmap_managed_page() to page_is_devmap_managed(), >> and limit the functionality to "read only": return a bool, >> with no side effects. >> >> * Add a new routine, put_devmap_managed_page(), to handle checking >> what kind of page it is, and what kind of refcount handling it >> requires. >> >> * Rename __put_devmap_managed_page() to free_devmap_managed_page(), >> and limit the functionality to unconditionally freeing a devmap >> page. > > What the reason to separate put_devmap_managed_page() from > free_devmap_managed_page() if free_devmap_managed_page() has exacly one > caller? Is it preparation for the next patches? Yes. A later patch, #23, adds another caller: __unpin_devmap_managed_user_page(). ... >> @@ -971,7 +971,14 @@ static inline bool put_devmap_managed_page(struct page *page) >> return false; >> } >> >> +bool put_devmap_managed_page(struct page *page); >> + >> #else /* CONFIG_DEV_PAGEMAP_OPS */ >> +static inline bool page_is_devmap_managed(struct page *page) >> +{ >> + return false; >> +} >> + >> static inline bool put_devmap_managed_page(struct page *page) >> { >> return false; >> @@ -1028,8 +1035,10 @@ static inline void put_page(struct page *page) >> * need to inform the device driver through callback. See >> * include/linux/memremap.h and HMM for details. >> */ >> - if (put_devmap_managed_page(page)) >> + if (page_is_devmap_managed(page)) { >> + put_devmap_managed_page(page); > > put_devmap_managed_page() has yet another page_is_devmap_managed() check > inside. It looks strange. > Good point, it's an extra unnecessary check. So to clean it up, I'll note that the "if" check is required here in put_page(), in order to stay out of non-inlined function calls in the hot path (put_page()). So I'll do the following: * Leave the above code as it is here * Simplify put_devmap_managed_page(), it was trying to do two separate things, and those two things have different requirements. So change it to a void function, with a WARN_ON_ONCE to assert that page_is_devmap_managed() is true, * And change the other caller (release_pages()) to do that check. ... >> @@ -1102,3 +1102,27 @@ void __init swap_setup(void) >> * _really_ don't want to cluster much more >> */ >> } >> + >> +#ifdef CONFIG_DEV_PAGEMAP_OPS >> +bool put_devmap_managed_page(struct page *page) >> +{ >> + bool is_devmap = page_is_devmap_managed(page); >> + >> + if (is_devmap) { > > Reversing the condition would save you an indentation level. Yes. Done. I'll also git-reply with an updated patch so you can see what it looks like. thanks, -- John Hubbard NVIDIA
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