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Date: Tue, 19 Feb 2013 18:32:36 +0800
From: Simon Jeons <simon.jeons@gmail.com>
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To: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
CC: Andrew Morton <akpm@linux-foundation.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Al Viro <viro@zeniv.linux.org.uk>, linux-mm@kvack.org,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        Wu Fengguang <fengguang.wu@intel.com>, Jan Kara <jack@suse.cz>,
        Nick Piggin <npiggin@kernel.dk>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Andi Kleen <ak@linux.intel.com>,
        "Kirill A. Shutemov" <kirill@shutemov.name>
Subject: Re: PAGE_CACHE_SIZE vs. PAGE_SIZE
References: <20130118155724.GA8507@otc-wbsnb-06>
In-Reply-To: <20130118155724.GA8507@otc-wbsnb-06>
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On 01/18/2013 11:57 PM, Kirill A. Shutemov wrote:
> Hi,
>
> PAGE_CACHE_* macros were introduced long time ago in hope to implement
> page cache with larger chunks than one page in future.
>
> In fact it was never done.
>
> Some code paths assume PAGE_CACHE_SIZE <= PAGE_SIZE. E.g. we use
> zero_user_segments() to clear stale parts of page on cache filling, but
> the function is implemented only for individual small page.
>
> It's unlikely that global switch to PAGE_CACHE_SIZE > PAGE_SIZE will never
> happen since it will affect to much code at once.
>
> I think support of larger chunks in page cache can be in implemented in
> some form of THP with per-fs enabling.

IIRC, you try to implement THP support page cache, then PAGE_CACHE_SIZE 
maybe don't need any more.

>
> Is it time to get rid of PAGE_CACHE_* macros?
> I can prepare patchset if it's okay.
>