linux-kernel - Re: [PATCHv4 20/39] thp, mm: naive support of thp in generic read/write routines

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Message-ID: <51B1FC4F.2020700@sr71.net>
Date:	Fri, 07 Jun 2013 08:29:19 -0700
From:	Dave Hansen <dave@...1.net>
To:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
CC:	Andrea Arcangeli <aarcange@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	Hugh Dickins <hughd@...gle.com>,
	Wu Fengguang <fengguang.wu@...el.com>, Jan Kara <jack@...e.cz>,
	Mel Gorman <mgorman@...e.de>, linux-mm@...ck.org,
	Andi Kleen <ak@...ux.intel.com>,
	Matthew Wilcox <matthew.r.wilcox@...el.com>,
	"Kirill A. Shutemov" <kirill@...temov.name>,
	Hillf Danton <dhillf@...il.com>, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCHv4 20/39] thp, mm: naive support of thp in generic read/write
 routines

On 06/07/2013 08:17 AM, Kirill A. Shutemov wrote:
<snip>
> I guess this way is better, right?
> 
> @@ -2382,6 +2393,7 @@ static ssize_t generic_perform_write(struct file *file,
>                 unsigned long bytes;    /* Bytes to write to page */
>                 size_t copied;          /* Bytes copied from user */
>                 void *fsdata;
> +               int subpage_nr = 0;
>  
>                 offset = (pos & (PAGE_CACHE_SIZE - 1));
>                 bytes = min_t(unsigned long, PAGE_CACHE_SIZE - offset,
> @@ -2411,8 +2423,14 @@ again:
>                 if (mapping_writably_mapped(mapping))
>                         flush_dcache_page(page);
>  
> +               if (PageTransHuge(page)) {
> +                       off_t huge_offset = pos & ~HPAGE_PMD_MASK;
> +                       subpage_nr = huge_offset >> PAGE_CACHE_SHIFT;
> +               }
> +
>                 pagefault_disable();
> -               copied = iov_iter_copy_from_user_atomic(page, i, offset, bytes);
> +               copied = iov_iter_copy_from_user_atomic(page + subpage_nr, i,
> +                               offset, bytes);
>                 pagefault_enable();
>                 flush_dcache_page(page);

That looks substantially easier to understand to me.  Nice.
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