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Message-ID: <de9a3db9-6130-fe07-88ec-7e728ff5701c@nvidia.com>
Date: Wed, 17 Aug 2022 13:35:12 -0700
From: John Hubbard <jhubbard@...dia.com>
To: Jason Gunthorpe <jgg@...dia.com>,
Alistair Popple <apopple@...dia.com>
Cc: linux-mm@...ck.org, akpm@...ux-foundation.org,
linux-kernel@...r.kernel.org,
"Sierra Guiza, Alejandro (Alex)" <alex.sierra@....com>,
Chaitanya Kulkarni <kch@...dia.com>,
Dan Williams <dan.j.williams@...el.com>,
Felix Kuehling <Felix.Kuehling@....com>,
Logan Gunthorpe <logang@...tatee.com>,
Miaohe Lin <linmiaohe@...wei.com>,
Muchun Song <songmuchun@...edance.com>,
Ralph Campbell <rcampbell@...dia.com>,
David Hildenbrand <david@...hat.com>,
Matthew Wilcox <willy@...radead.org>
Subject: Re: [PATCH v4 2/2] mm/gup.c: Refactor
check_and_migrate_movable_pages()
On 8/17/22 05:09, Jason Gunthorpe wrote:
>>> if (!ret) == if (ret != 0)
>>
>> Huh? Unless I'm misinterpretting you or am really behind on coffee
>> if (!ret) is equivalent to if (ret == 0), not if (ret != 0).
Although the !ret idiom is a huge, huge part of kernel coding practice,
it also adds a slight bit of unnecessary mental translation (go ahead,
flame me hard, I know I'm asking for it...but...see above, after all.
Pixels have been spilt working through it).
And also...
>
> Oh Dear, maybe I am still a bit jetlagged
>
> Regardless, it is confusingly written :)
>
...this is a slightly tricky and unusual error case, so it helps to be
extra clear by comparing against zero, and even adding a few short comments.
How's this look to you:
collected = collect_longterm_unpinnable_pages(&movable_page_list,
nr_pages, pages);
if (collected == 0)
return 0;
ret = migrate_longterm_unpinnable_pages(&movable_page_list, nr_pages,
pages);
/* If we got here, we have some unpinnable pages... */
if (ret == 0) {
/*
* ...and we successfully migrated those pages. Which means that
* the caller should retry the operation now.
*/
ret = -EAGAIN;
}
return ret;
thanks,
--
John Hubbard
NVIDIA
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