linux-kernel - Re: [PATCH 1/6] filemap: make the folio order calculation shareable

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Date:   Fri, 15 Sep 2023 14:40:07 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Daniel Gomez <da.gomez@...sung.com>
Cc:     "minchan@...nel.org" <minchan@...nel.org>,
        "senozhatsky@...omium.org" <senozhatsky@...omium.org>,
        "axboe@...nel.dk" <axboe@...nel.dk>,
        "djwong@...nel.org" <djwong@...nel.org>,
        "hughd@...gle.com" <hughd@...gle.com>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "mcgrof@...nel.org" <mcgrof@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        "linux-xfs@...r.kernel.org" <linux-xfs@...r.kernel.org>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "gost.dev@...sung.com" <gost.dev@...sung.com>,
        Pankaj Raghav <p.raghav@...sung.com>
Subject: Re: [PATCH 1/6] filemap: make the folio order calculation shareable

On Fri, Sep 15, 2023 at 09:51:23AM +0000, Daniel Gomez wrote:
> To make the code that clamps the folio order in the __filemap_get_folio
> routine reusable to others, move and merge it to the fgf_set_order
> new subroutine (mapping_size_order), so when mapping the size at a
> given index, the order calculated is already valid and ready to be
> used when order is retrieved from fgp_flags with FGF_GET_ORDER.
> 
> Signed-off-by: Daniel Gomez <da.gomez@...sung.com>
> ---
>  fs/iomap/buffered-io.c  |  6 ++++--
>  include/linux/pagemap.h | 42 ++++++++++++++++++++++++++++++++++++-----
>  mm/filemap.c            |  8 --------
>  3 files changed, 41 insertions(+), 15 deletions(-)

That seems like a lot of extra code to add in order to avoid copying
six lines of code and one comment into the shmem code.

It's not wrong, but it seems like a bad tradeoff to me.