On Tue, Jul 31, 2012 at 9:42 AM, Guangliang Zhao <gzhao@xxxxxxxx> wrote:
> On Mon, Jul 30, 2012 at 02:54:44PM -0700, Yehuda Sadeh wrote:
>> On Thu, Jul 26, 2012 at 11:20 PM, Guangliang Zhao <gzhao@xxxxxxxx> wrote:
>> > The bio_pair alloced in bio_chain_clone would not be freed,
>> > this will cause a memory leak. It could be freed actually only
>> > after 3 times release, because the reference count of bio_pair
>> > is initialized to 3 when bio_split and bio_pair_release only
>> > drops the reference count.
>> >
>> > The function bio_pair_release must be called three times for
>> > releasing bio_pair, and the callback functions of bios on the
>> > requests will be called when the last release time in bio_pair_release,
>> > however, these functions will also be called in rbd_req_cb. In
>> > other words, they will be called twice, and it may cause serious
>> > consequences.
>> >
>> > This patch clones bio chian from the origin directly, doesn't use
>> > bio_split(without bio_pair). The new bio chain can be release
>> > whenever we don't need it.
>> >
>> > Signed-off-by: Guangliang Zhao <gzhao@xxxxxxxx>
>> > ---
>> > drivers/block/rbd.c | 73 +++++++++++++++++++++-----------------------------
>> > 1 files changed, 31 insertions(+), 42 deletions(-)
>> >
>> > diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
>> > index 013c7a5..356657d 100644
>> > --- a/drivers/block/rbd.c
>> > +++ b/drivers/block/rbd.c
>> > @@ -712,51 +712,46 @@ static void zero_bio_chain(struct bio *chain, int start_ofs)
>> > }
>> > }
>> >
>> > -/*
>> > - * bio_chain_clone - clone a chain of bios up to a certain length.
>> > - * might return a bio_pair that will need to be released.
>> > +/**
>> > + * bio_chain_clone - clone a chain of bios up to a certain length.
>> > + * @old: bio to clone
>> > + * @offset: start point for bio clone
>> > + * @len: length of bio chain
>> > + * @gfp_mask: allocation priority
>> > + *
>> > + * RETURNS:
>> > + * Pointer to new bio chain on success, NULL on failure.
>> > */
>> > -static struct bio *bio_chain_clone(struct bio **old, struct bio **next,
>> > - struct bio_pair **bp,
>> > +static struct bio *bio_chain_clone(struct bio **old, int *offset,
>> > int len, gfp_t gfpmask)
>> > {
>> > struct bio *tmp, *old_chain = *old, *new_chain = NULL, *tail = NULL;
>> > int total = 0;
>> >
>> > - if (*bp) {
>> > - bio_pair_release(*bp);
>> > - *bp = NULL;
>> > - }
>> > -
>> > while (old_chain && (total < len)) {
>> > + int need = len - total;
>> > +
>> > tmp = bio_kmalloc(gfpmask, old_chain->bi_max_vecs);
>> > if (!tmp)
>> > goto err_out;
>> >
>> > - if (total + old_chain->bi_size > len) {
>> > - struct bio_pair *bp;
>> > -
>> > - /*
>> > - * this split can only happen with a single paged bio,
>> > - * split_bio will BUG_ON if this is not the case
>> > - */
>> > - dout("bio_chain_clone split! total=%d remaining=%d"
>> > - "bi_size=%d\n",
>> > - (int)total, (int)len-total,
>> > - (int)old_chain->bi_size);
>> > -
>> > - /* split the bio. We'll release it either in the next
>> > - call, or it will have to be released outside */
>> > - bp = bio_split(old_chain, (len - total) / SECTOR_SIZE);
>> > - if (!bp)
>> > - goto err_out;
>> > -
>> > - __bio_clone(tmp, &bp->bio1);
>> > -
>> > - *next = &bp->bio2;
>> > + __bio_clone(tmp, old_chain);
>> > + tmp->bi_sector += *offset >> SECTOR_SHIFT;
>> > + tmp->bi_io_vec->bv_offset += *offset >> SECTOR_SHIFT;
>> > + /*
>> > + * The bios span across multiple osd objects must be
>> > + * single paged, rbd_merge_bvec would guarantee it.
>> > + * So we needn't worry about other things.
>> > + */
>> > + if (tmp->bi_size - *offset > need) {
>> > + tmp->bi_size = need;
>> > + tmp->bi_io_vec->bv_len = need;
>> > + *offset += need;
>> > } else {
>> > - __bio_clone(tmp, old_chain);
>> > - *next = old_chain->bi_next;
>> > + old_chain = old_chain->bi_next;
>> > + tmp->bi_size -= *offset;
>> > + tmp->bi_io_vec->bv_len -= *offset;
>> > + *offset = 0;
>> > }
>> >
>> There's still some inherent issue here, which is it assumes
>> tmp->bi_io_vec points to the only iovec for this bio. I don't think
>> that is necessarily true, there may be multiple iovecs,
>
> Yes, the bios on the requests may have one or more pages, but the ones span across
> multiple osds *must* be single page bios because of rbd_merge_bvec.
>
> With rbd_merge_bvec, the new bvec will not permitted to merge, if it make the bio cross
> the osd boundary, except the bvec is the first one. In other words, there are two
> types of bio:
>
> 1) The bios don't cross the osd boundary, they may have several iovecs.
> The value of offset will always be 0 in this case, so nothing will be changed, and
> the code changes tmp bios doesn't take effact at all.
>
> 2) The bios cross the osd boundary, each one have only one page.
> These bios need to be split in this case, and the offset is used to indicate the next bio,
> it makes sense only in this instance. The orgin code use bio_split which can only handle
> single page bios too.
>
> So, you maybe worry about the multiple iovecs bios. They wouldn't cross the osd boundary,
> offset is always 0, so tmp bios are as same as the orgins. The needn't and wouldn't to
> be changed.
>
> Thanks for your reply :).
>
Yeah, thinking about it, I think you're right. Maybe that comment
should be improved a bit, explaining this?
Thanks,
Yehuda
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