Hi Shaohua,
On Wed, Mar 1, 2017 at 7:30 AM, Shaohua Li <s...@kernel.org> wrote:
> On Tue, Feb 28, 2017 at 11:41:34PM +0800, Ming Lei wrote:
>> Now resync I/O use bio's bec table to manage pages,
>> this way is very hacky, and may not work any more
>> once multipage bvec is introduced.
>>
>> So introduce helpers and new data structure for
>> managing resync I/O pages more cleanly.
>>
>> Signed-off-by: Ming Lei <tom.leim...@gmail.com>
>> ---
>> drivers/md/md.h | 54 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
>> 1 file changed, 54 insertions(+)
>>
>> diff --git a/drivers/md/md.h b/drivers/md/md.h
>> index 1d63239a1be4..b5a638d85cb4 100644
>> --- a/drivers/md/md.h
>> +++ b/drivers/md/md.h
>> @@ -720,4 +720,58 @@ static inline void mddev_check_writesame(struct mddev
>> *mddev, struct bio *bio)
>> #define RESYNC_BLOCK_SIZE (64*1024)
>> #define RESYNC_PAGES ((RESYNC_BLOCK_SIZE + PAGE_SIZE-1) / PAGE_SIZE)
>>
>> +/* for managing resync I/O pages */
>> +struct resync_pages {
>> + unsigned idx; /* for get/put page from the pool */
>> + void *raid_bio;
>> + struct page *pages[RESYNC_PAGES];
>> +};
>
> I'd like this to be embedded into r1bio directly. Not sure if we really need a
> structure.
There are two reasons we can't put this into r1bio:
- r1bio is used in both normal and resync I/O, not fair to allocate more
in normal I/O, and that is why this patch wouldn't like to touch r1bio or r10bio
- the count of 'struct resync_pages' instance depends on raid_disks(raid1)
or copies(raid10), both can't be decided during compiling.
>
>> +
>> +static inline int resync_alloc_pages(struct resync_pages *rp,
>> + gfp_t gfp_flags)
>> +{
>> + int i;
>> +
>> + for (i = 0; i < RESYNC_PAGES; i++) {
>> + rp->pages[i] = alloc_page(gfp_flags);
>> + if (!rp->pages[i])
>> + goto out_free;
>> + }
>> +
>> + return 0;
>> +
>> + out_free:
>> + while (--i >= 0)
>> + __free_page(rp->pages[i]);
>> + return -ENOMEM;
>> +}
>> +
>> +static inline void resync_free_pages(struct resync_pages *rp)
>> +{
>> + int i;
>> +
>> + for (i = 0; i < RESYNC_PAGES; i++)
>> + __free_page(rp->pages[i]);
>
> Since we will use get_page, shouldn't this be put_page?
You are right, will fix in v3.
>
>> +}
>> +
>> +static inline void resync_get_all_pages(struct resync_pages *rp)
>> +{
>> + int i;
>> +
>> + for (i = 0; i < RESYNC_PAGES; i++)
>> + get_page(rp->pages[i]);
>> +}
>> +
>> +static inline struct page *resync_fetch_page(struct resync_pages *rp)
>> +{
>> + if (WARN_ON_ONCE(rp->idx >= RESYNC_PAGES))
>> + return NULL;
>> + return rp->pages[rp->idx++];
>
> I'd like the caller explicitly specify the index instead of a global variable
> to track it, which will make the code more understandable and less error
> prone.
That is fine, but the index has to be per bio, and finally the index
has to be stored
in 'struct resync_pages', so every user has to call it in the following way:
resync_fetch_page(rp, rp->idx);
then looks no benefit to pass index explicitly.
>
>> +}
>> +
>> +static inline bool resync_page_available(struct resync_pages *rp)
>> +{
>> + return rp->idx < RESYNC_PAGES;
>> +}
>
> Then we don't need this obscure API.
That is fine.
Thanks,
Ming Lei
