Re: [PATCH 0/8] mm: globalize rest_of_page() macro

From: Jens Axboe <axboe@kernel.dk>
To: Yury Norov <ynorov@nvidia.com>, Sean Christopherson <seanjc@google.com>
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Subject: Re: [PATCH 0/8] mm: globalize rest_of_page() macro
Date: Tue, 3 Mar 2026 20:35:01 -0700	[thread overview]
Message-ID: <e96e851a-9050-4d8c-b1e5-bc3b5d91a84c@kernel.dk> (raw)
In-Reply-To: <aaen2pGs0UeiJqz1@yury>

On 3/3/26 8:32 PM, Yury Norov wrote:
> My motivation is that it helps to simplify constructions like this:
> 
> -               loff_t cmp_len = min(PAGE_SIZE - offset_in_page(srcoff),
> -                                    PAGE_SIZE - offset_in_page(dstoff));
> +               loff_t cmp_len = min(rest_of_page(srcoff), rest_of_page(dstoff));
> 
> Or this:
> 
> -               if (folio_test_highmem(dst_folio) &&
> -                   chunk > PAGE_SIZE - offset_in_page(dst_off))
> -                       chunk = PAGE_SIZE - offset_in_page(dst_off);
> -               if (folio_test_highmem(src_folio) &&
> -                   chunk > PAGE_SIZE - offset_in_page(src_off))
> -                       chunk = PAGE_SIZE - offset_in_page(src_off);
> +               if (folio_test_highmem(dst_folio) && chunk > rest_of_page(dst_off))
> +                       chunk = rest_of_page(dst_off);
> +               if (folio_test_highmem(src_folio) && chunk > rest_of_page(src_off))
> +                       chunk = rest_of_page(src_off);
> 
> To a point where I don't have to use my brains to decode them. I agree
> it's an easy math. It's just too bulky to my (and 9p guys too) taste.

The thing is, now I have to go lookup what on earth rest_of_page() does,
whereas PAGE_SIZE - offset_in_page(page) is immediately obvious. It's a
classic case of "oh let's add this helper to simplify things" which
really just makes it worse, because now you have to jump to the
definition of rest_of_page().

IOW, just no.

-- 
Jens Axboe