2008-07-11 23:39:36

by Andrew Morton

[permalink] [raw]
Subject: Re: [PATCH] VFS: Pagecache usage optimization onpagesize!=blocksize environment

On Tue, 27 May 2008 18:34:02 +0900 Hisashi Hifumi <[email protected]> wrote:

> When we read some part of a file through pagecache, if there is a pagecache
> of corresponding index but this page is not uptodate, read IO is issued and
> this page will be uptodate.
> I think this is good for pagesize == blocksize environment but there is room
> for improvement on pagesize != blocksize environment. Because in this case
> a page can have multiple buffers and even if a page is not uptodate, some buffers
> can be uptodate. So I suggest that when all buffers which correspond to a part
> of a file that we want to read are uptodate, use this pagecache and copy data
> from this pagecache to user buffer even if a page is not uptodate. This can
> reduce read IO and improve system throughput.
> v2: add new address_space_operations member is_partially_uptodate, and
> block_is_partially_uptodate was registered to ext2/3/4's aops.
> modify do_generic_file_read to use this aops callback.
> v3: use unsigned instead of unsigned long in block_is_partially_uptodate.
> cleaned up and simplified page buffer iteration code in block_is_partially_uptodate.
> Signed-off-by :Hisashi Hifumi <[email protected]>

ext4 has now gained a new set of address_space_operations:
ext4_da_aops. I put a

.is_partially_uptodate = block_is_partially_uptodate,

into there as well, but I have no clue whether it will work OK.