[dpdk-dev] [PATCH 2/2] mempool: fix pages computation to determine number of objects
Adrien Mazarguil
adrien.mazarguil at 6wind.com
Tue May 26 11:14:18 CEST 2015
On Mon, May 25, 2015 at 06:20:03PM +0000, Ananyev, Konstantin wrote:
> Hi Adrien,
Hi Konstantin,
> > -----Original Message-----
> > From: dev [mailto:dev-bounces at dpdk.org] On Behalf Of Adrien Mazarguil
> > Sent: Monday, May 25, 2015 5:28 PM
> > To: dev at dpdk.org
> > Subject: [dpdk-dev] [PATCH 2/2] mempool: fix pages computation to determine number of objects
> >
> > In rte_mempool_obj_iter(), even when a single page is required per object,
> > a loop checks that the the next page is contiguous and drops the first one
> > otherwise. This commit checks subsequent pages only when several are
> > required per object.
> >
> > Also a minor fix for the amount of remaining space that prevents using the
> > entire region.
> >
> > Fixes: 148f963fb532 ("xen: core library changes")
> >
> > Signed-off-by: Adrien Mazarguil <adrien.mazarguil at 6wind.com>
> > ---
> > lib/librte_mempool/rte_mempool.c | 11 ++++++++---
> > 1 file changed, 8 insertions(+), 3 deletions(-)
> >
> > diff --git a/lib/librte_mempool/rte_mempool.c b/lib/librte_mempool/rte_mempool.c
> > index d1a02a2..3c1efec 100644
> > --- a/lib/librte_mempool/rte_mempool.c
> > +++ b/lib/librte_mempool/rte_mempool.c
> > @@ -175,12 +175,17 @@ rte_mempool_obj_iter(void *vaddr, uint32_t elt_num, size_t elt_sz, size_t align,
> > pgn += j;
> >
> > /* do we have enough space left for the next element. */
> > - if (pgn >= pg_num)
> > + if (pgn > pg_num)
> > break;
>
> Hmm, that doesn't look right.
> Suppose:
> start==0; end==5120; pg_shift==12; pg_num == 1;
> So:
> pgn = 1; // (5120>>12)-(0>>12)
>
> And we end-up accessing element that is beyond allocated memory.
>
> >
> > - for (k = j;
> > + /*
> > + * Compute k so that (k - j) is the number of contiguous
> > + * pages starting from index j. Note that there is at least
> > + * one page.
> > + */
> > + for (k = j + 1;
> > k != pgn &&
> > - paddr[k] + pg_sz == paddr[k + 1];
> > + paddr[k - 1] + pg_sz == paddr[k];
> > k++)
> > ;
>
>
> Again, suppose:
> j==0; start==0; end==2048; pg_shift==12; pg_num == 2;
> So:
> pgn = 0;
> k = 1;
> and the loop goes beyond paddr[] boundaries.
>
> The problem here, I think that you treat pgn as number of pages, while it is index of last page to be used.
Well, I misunderstood the logic here, to me pgn was the number of pages
necessary for the current object on top of the number of pages used so
far. Assuming a single object uses at least one page (assuming 4K pages),
pgn wasn't supposed to be zero.
> As I understand, what you are trying to fix here, is a situation when end is a multiply of page size (end == N * pg_sz), right?
This and also when (end - start) < page size.
> Then, probably something simple like that would do:
>
> - pgn = (end >> pg_shift) - (start >> pg_shift);
> + pgn = (end - 1 >> pg_shift) - (start >> pg_shift);
> + pg_next = (end >> pg_shift) - (start >> pg_shift);
> ...
> if (k == pgn) {
> if (obj_iter != NULL)
> obj_iter(obj_iter_arg, (void *)start,
> (void *)end, i);
> va = end;
> - j = pgn;
> + j = pg_next;
> i++;
> } else {
> ...
That does not seem to be enough to solve the issue in my scenario, I get
weird results (j never reaches pg_num).
I'll come up with a new patch that takes your comment into account,
hopefully covering all cases.
Thanks,
--
Adrien Mazarguil
6WIND
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