[dpdk-dev,v2,2/2] mem: unmap unneeded space
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Commit Message
When we ask to reserve virtual areas, we usually include
alignment in the mapping size, and that memory ends up
being wasted. Wasting a gigabyte of VA space while trying to
reserve one gigabyte is pretty expensive on 32-bit, so after
we're done mapping, unmap unneeded space.
Signed-off-by: Anatoly Burakov <anatoly.burakov@intel.com>
---
Notes:
v2:
- Split fix for size_t overflow into separate patch
- Improve readability of unmapping code
- Added comment explaining why unmapping is done
lib/librte_eal/common/eal_common_memory.c | 26 +++++++++++++++++++++++++-
1 file changed, 25 insertions(+), 1 deletion(-)
Comments
On Mon, Apr 30, 2018 at 12:21:43PM +0100, Anatoly Burakov wrote:
> When we ask to reserve virtual areas, we usually include
> alignment in the mapping size, and that memory ends up
> being wasted. Wasting a gigabyte of VA space while trying to
> reserve one gigabyte is pretty expensive on 32-bit, so after
> we're done mapping, unmap unneeded space.
>
> Signed-off-by: Anatoly Burakov <anatoly.burakov@intel.com>
> ---
>
> Notes:
> v2:
> - Split fix for size_t overflow into separate patch
> - Improve readability of unmapping code
> - Added comment explaining why unmapping is done
>
Acked-by: Bruce Richardson <bruce.richardson@intel.com>
30/04/2018 14:50, Bruce Richardson:
> On Mon, Apr 30, 2018 at 12:21:43PM +0100, Anatoly Burakov wrote:
> > When we ask to reserve virtual areas, we usually include
> > alignment in the mapping size, and that memory ends up
> > being wasted. Wasting a gigabyte of VA space while trying to
> > reserve one gigabyte is pretty expensive on 32-bit, so after
> > we're done mapping, unmap unneeded space.
> >
> > Signed-off-by: Anatoly Burakov <anatoly.burakov@intel.com>
> > ---
> >
> > Notes:
> > v2:
> > - Split fix for size_t overflow into separate patch
> > - Improve readability of unmapping code
> > - Added comment explaining why unmapping is done
> >
> Acked-by: Bruce Richardson <bruce.richardson@intel.com>
I am not confident pushing this change post-rc1.
Please can we have more validation tests with this patch?
02/05/2018 23:00, Thomas Monjalon:
> 30/04/2018 14:50, Bruce Richardson:
> > On Mon, Apr 30, 2018 at 12:21:43PM +0100, Anatoly Burakov wrote:
> > > When we ask to reserve virtual areas, we usually include
> > > alignment in the mapping size, and that memory ends up
> > > being wasted. Wasting a gigabyte of VA space while trying to
> > > reserve one gigabyte is pretty expensive on 32-bit, so after
> > > we're done mapping, unmap unneeded space.
> > >
> > > Signed-off-by: Anatoly Burakov <anatoly.burakov@intel.com>
> > > ---
> > >
> > > Notes:
> > > v2:
> > > - Split fix for size_t overflow into separate patch
> > > - Improve readability of unmapping code
> > > - Added comment explaining why unmapping is done
> > >
> > Acked-by: Bruce Richardson <bruce.richardson@intel.com>
>
> I am not confident pushing this change post-rc1.
> Please can we have more validation tests with this patch?
Any news about validation tests?
08/05/2018 22:20, Thomas Monjalon:
> 02/05/2018 23:00, Thomas Monjalon:
> > 30/04/2018 14:50, Bruce Richardson:
> > > On Mon, Apr 30, 2018 at 12:21:43PM +0100, Anatoly Burakov wrote:
> > > > When we ask to reserve virtual areas, we usually include
> > > > alignment in the mapping size, and that memory ends up
> > > > being wasted. Wasting a gigabyte of VA space while trying to
> > > > reserve one gigabyte is pretty expensive on 32-bit, so after
> > > > we're done mapping, unmap unneeded space.
> > > >
> > > > Signed-off-by: Anatoly Burakov <anatoly.burakov@intel.com>
> > > > ---
> > > >
> > > > Notes:
> > > > v2:
> > > > - Split fix for size_t overflow into separate patch
> > > > - Improve readability of unmapping code
> > > > - Added comment explaining why unmapping is done
> > > >
> > > Acked-by: Bruce Richardson <bruce.richardson@intel.com>
> >
> > I am not confident pushing this change post-rc1.
> > Please can we have more validation tests with this patch?
>
> Any news about validation tests?
No news, but I've decided to push it anyway.
Series applied
@@ -121,8 +121,32 @@ eal_get_virtual_area(void *requested_addr, size_t *size,
RTE_LOG(DEBUG, EAL, "Virtual area found at %p (size = 0x%zx)\n",
aligned_addr, *size);
- if (unmap)
+ if (unmap) {
munmap(mapped_addr, map_sz);
+ } else if (!no_align) {
+ void *map_end, *aligned_end;
+ size_t before_len, after_len;
+
+ /* when we reserve space with alignment, we add alignment to
+ * mapping size. On 32-bit, if 1GB alignment was requested, this
+ * would waste 1GB of address space, which is a luxury we cannot
+ * afford. so, if alignment was performed, check if any unneeded
+ * address space can be unmapped back.
+ */
+
+ map_end = RTE_PTR_ADD(mapped_addr, (size_t)map_sz);
+ aligned_end = RTE_PTR_ADD(aligned_addr, *size);
+
+ /* unmap space before aligned mmap address */
+ before_len = RTE_PTR_DIFF(aligned_addr, mapped_addr);
+ if (before_len > 0)
+ munmap(mapped_addr, before_len);
+
+ /* unmap space after aligned end mmap address */
+ after_len = RTE_PTR_DIFF(map_end, aligned_end);
+ if (after_len > 0)
+ munmap(aligned_end, after_len);
+ }
baseaddr_offset += *size;