review request for 7142641: -Xshared:on fails on ARM

[Daniel D. Daugherty]

Dean,

I'm confused... I thought mapping the read-only CDS archive pages as
"shared" permits those pages to be shared by other java processes that
are also using the CDS archive...

Dan

On 2/28/12 3:05 PM, Dean Long wrote:
> http://cr.openjdk.java.net/~dlong/7142641/webrev.0/
> Summary of changes:    3 lines changed: 0 ins; 2 del; 1 mod; 5538 unchg
>
> The Class Data Sharing file is mapped "shared" on linux, which places 
> extra constraints on which virtual address a file offset can use.  
> This is to ensure consistency on certain platforms with aliasing 
> caches.  However as the CDS file is opened read-only, mapping it 
> "shared" has no benefit and can cause the mmap to fail.  The simplest 
> fix is to change the mapping to "private".
>
> Tested on linux arm platform with aliasing cache.  Installed CDS with 
> -Xshare:dump then ran through some vm tests as a sanity check.
>
> This bug is on the 7u4 watch list.
>
> dl