Re: [dpdk-dev] [PATCH 9/9] memalloc: allocate memory in reverse

[Thomas Monjalon <thomas@monjalon.net>]

24/07/2018 12:10, Burakov, Anatoly:
> On 11-Jun-18 9:55 PM, Anatoly Burakov wrote:
> > Currently, all hugepages are allocated from lower VA address to
> > higher VA address, while malloc heap allocates from higher VA
> > address to lower VA address. This results in heap fragmentation
> > over time due to multiple reserves leaving small space below the
> > allocated elements.
> > 
> > Fix this by allocating VA memory from the top, thereby reducing
> > fragmentation and lowering overall memory usage.
> > 
> > Signed-off-by: Anatoly Burakov <anatoly.burakov@intel.com>
> > ---
> >   lib/librte_eal/linuxapp/eal/eal_memalloc.c | 3 ++-
> >   1 file changed, 2 insertions(+), 1 deletion(-)
> > 
> > diff --git a/lib/librte_eal/linuxapp/eal/eal_memalloc.c b/lib/librte_eal/linuxapp/eal/eal_memalloc.c
> > index 8c11f98c9..d35fb52c4 100644
> > --- a/lib/librte_eal/linuxapp/eal/eal_memalloc.c
> > +++ b/lib/librte_eal/linuxapp/eal/eal_memalloc.c
> > @@ -682,7 +682,8 @@ alloc_seg_walk(const struct rte_memseg_list *msl, void *arg)
> >   	need = wa->n_segs;
> >   
> >   	/* try finding space in memseg list */
> > -	cur_idx = rte_fbarray_find_next_n_free(&cur_msl->memseg_arr, 0, need);
> > +	cur_idx = rte_fbarray_find_prev_n_free(&cur_msl->memseg_arr,
> > +			cur_msl->memseg_arr.len - 1, need);
> >   	if (cur_idx < 0)
> >   		return 0;
> >   	start_idx = cur_idx;
> > 
> 
> Hi Thomas,
> 
> We have discovered a few regressions in virtio/vhost use cases due to 
> this patch. Virtio expects to map all segments starting from 0 address, 
> and this patch breaks that assumption.
> 
> Can we revert this for 18.08? It will be reintroduced in 18.11 along 
> with fixes for virtio/vhost fixes to account for this change.

Yes, please send the patch with explanations.