linux-kernel - Re: [PATCH 16/21] sysfs: implement bin

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Message-ID: <a781481a0705011237n791f7cafn54509c1a41cf3de6@mail.gmail.com>
Date:	Wed, 2 May 2007 01:07:48 +0530
From:	"Satyam Sharma" <satyam.sharma@...il.com>
To:	"Tejun Heo" <htejun@...il.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 16/21] sysfs: implement bin_buffer

(We went off-list just now. Adding lkml again.)

On 5/1/07, Tejun Heo <htejun@...il.com> wrote:
> Satyam Sharma wrote:
> > On 4/28/07, Tejun Heo <htejun@...il.com> wrote:
> >> Implement bin_buffer which contains a mutex and pointer to PAGE_SIZE
> >> buffer to properly synchronize accesses to per-openfile buffer and
> >> prepare for immediate-kobj-disconnect.
> >>
> >> Signed-off-by: Tejun Heo <htejun@...il.com>
> >> ---
> >> [...]
> >> @@ -135,14 +160,22 @@ static int open(struct inode * inode, struct
> >> file * file)
> >>                 goto Error;
> >>
> >>         error = -ENOMEM;
> >> -       file->private_data = kmalloc(PAGE_SIZE, GFP_KERNEL);
> >> -       if (!file->private_data)
> >> +       bb = kzalloc(sizeof(*bb), GFP_KERNEL);
> >> +       if (!bb)
> >>                 goto Error;
> >>
> >> +       bb->buffer = kmalloc(PAGE_SIZE, GFP_KERNEL);
> >
> > You could simply do a __get_free_page() here instead of a
> > kmalloc(PAGE_SIZE).
>
> Yes, I could but 1. the original code was done using kmalloc

Yes, I saw that, but you could change it just as well. In any case,
this will only make fs/sysfs/bin.c similar to what is being done in
fs/sysfs/file.c. We allocate the buffer page backing the attribute's
data in fill_read_buffer() and fill_write_buffer() using
get_zeroed_page() and not kzalloc().

> 2. I'm not sure __get_free_page() is better than kmalloc(PAGE_SIZE, ), is it?

If you know for sure that you require *exactly* PAGE_SIZE bytes, then
yes, it is.
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