Hi,
On 05/28/2010 11:05 PM, Dan Magenheimer wrote:
> [PATCH V2 2/7] Cleancache (was Transcendent Memory): core files
I just finished a rough (but working) implementation of in-kernel
page cache compression backend (called zcache). During this work,
I found some issues with cleancache, mostly related to (lack of)
comments/documentation:
> +
> +static inline int cleancache_init_fs(size_t pagesize)
> +
- It is not very obvious that this function is called when
an instance of cleancache supported filesystem is *mounted*.
Initially, I thought this is called which any such filesystem
module is loaded.
- It seems that returning pool_id of 0 is considered as error
condition (as it appears from deactivate_locked_super() changes).
This seems weird; I think only negative pool_id should considered
as error. Anyway, please add function comments for these.
> +int __cleancache_get_page(struct page *page)
> +{
> + int ret = 0;
> + int pool_id = page->mapping->host->i_sb->cleancache_poolid;
> +
> + if (pool_id >= 0) {
> + ret = (*cleancache_ops->get_page)(pool_id,
> + page->mapping->host->i_ino,
> + page->index,
> + page);
> + if (ret == CLEANCACHE_GET_PAGE_SUCCESS)
> + succ_gets++;
> + else
> + failed_gets++;
> + }
> + return ret;
> +}
It seems "non-standard" to use '1' as success code. You could simply use
0 for success and negative error code as failure. Then you can also get
rid of CLEANCACHE_GET_PAGE_SUCCESS.
> +
> +int __cleancache_put_page(struct page *page)
What return values stands for successful put? 1? Anyway, following the
same, 0 for success, negative codes for errors, seems to be better.
> +
> +int __cleancache_flush_page(struct address_space *mapping, struct page *page)
> +int __cleancache_flush_inode(struct address_space *mapping)
Return values for all the flush functions is ignored everywhere, so
why not make them return void instead?
> +static inline void cleancache_flush_fs(int pool_id)
Like init_fs, please document that it is called when a cleancache
aware filesystem is unmounted (or in other cases too?).
Page cache compression was a long-pending project. I'm glad its
coming into shape with the help of cleancache :)
Thanks,
Nitin
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