Replacing a page in page_cache

Replacing a page in page_cache

[Jack David]

Hi All,

I am trying to replace a page which is already present in page_cache.
Is there any direct way to do so (via some kernel API)?  My experiment
is something like, I have a file opened and read completely in user
space app (just to make sure that all the file is present in page
cache). From kernel, I am allocating a new page, filling some data
into it, and want to store this data by replacing some existing page
from page_cache.

Initially I was thinking of removing a page (at a particular index)
from page_cache and then add my new page at the same index. But by
doing so, that page will be treated as containing invalid data, hence
again the data will be fetched from the disk and it will overwrite
whatever I had initially written into that page. Is there any way I
can add the page into page_cache (by add_to_page_cache_lru) and still
mark it Uptodate (SetPageUptodate or something) without any bad
consequences?

Regards,
Jack

Replacing a page in page_cache

[Mulyadi Santosa]

On Mon, Feb 27, 2012 at 20:41, Jack David <jd6589@gmail.com> wrote:
> Hi All,
>
> I am trying to replace a page which is already present in page_cache.
> Is there any direct way to do so (via some kernel API)? ?My experiment
> is something like, I have a file opened and read completely in user
> space app (just to make sure that all the file is present in page
> cache). From kernel, I am allocating a new page, filling some data
> into it, and want to store this data by replacing some existing page
> from page_cache.

sounds like what you want to do is like normal mmap in user space and
then write new data into it?

-- 
regards,

Mulyadi Santosa
Freelance Linux trainer and consultant

blog: the-hydra.blogspot.com
training: mulyaditraining.blogspot.com

Replacing a page in page_cache

[Jack David]

On Tue, Feb 28, 2012 at 2:50 AM, Mulyadi Santosa
<mulyadi.santosa@gmail.com> wrote:
> On Mon, Feb 27, 2012 at 20:41, Jack David <jd6589@gmail.com> wrote:
>> Hi All,
>>
>> I am trying to replace a page which is already present in page_cache.
>> Is there any direct way to do so (via some kernel API)? ?My experiment
>> is something like, I have a file opened and read completely in user
>> space app (just to make sure that all the file is present in page
>> cache). From kernel, I am allocating a new page, filling some data
>> into it, and want to store this data by replacing some existing page
>> from page_cache.
>
> sounds like what you want to do is like normal mmap in user space and
> then write new data into it?
>

Actually I want to share the pages (present in page cache) between two
files. I want to avoid memcopy in kernel as much as possible. I am
going through the mmap implementation in kernel but not able to
understand how it can help me in my scenario.

J