On Fri, Mar 3, 2017 at 1:55 AM, Shaohua Li <s...@kernel.org> wrote:
> On Thu, Mar 02, 2017 at 10:09:14AM +0800, Ming Lei wrote:
>> 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.
>
> Yes, I said it should be a pointer of r1bio pointing to the pages in other
> emails.
OK, got it, :-)
Actually I did that in my local tree, and finally I figured out not
necessary to introduce this pointor, which only usage is for freeing,
and we can get the
pointor from .bi_private of the 1st bio. And this stuff can be commented
clearly.
>
>> >
>> >> +}
>> >> +
>> >> +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
>
>> >
>> >> +
>> >> +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.
>
> I suppose the callers always iterate though page 0 to RESYNC_PAGES - 1. Then
> the callers can use an index by themselves. That will clearly show which page
> the callers are using. The resync_fetch_page() wrap is a blackbox we always
> need to refer to the definition.
OK, understood.
Thanks,
Ming Lei
