RFC (M): Purge ShenandoahVerifyReadsToFromSpace

[Aleksey Shipilev]

Ping.

On 04/17/2017 07:08 PM, Aleksey Shipilev wrote:
> Hi,
> 
> I was looking into our mprotect verification mechanics, and had the suspicion
> that verifying reads from from-space is dubious. Mostly because we do have
> legitimate cases where we strip read barriers and can do from-space reads
> without breaking semantics (e.g. final fields).
> 
> This seems to be partially catered by emitting more read barriers when
> ShenandoahVerifyReadsToFromSpace is enabled? It is double-dubious to me that
> verification code adds new barriers, thus hiding the potential issues.
> 
> Therefore, I propose we purge the VerifyReads part:
>   http://cr.openjdk.java.net/~shade/shenandoah/purge-verifyreads/webrev.01/
> 
> Or maybe there is some legitimate use that outweights the costs?
> 
> Testing: hotspot_gc_shenandoah
> 
> Thanks,
> -Aleksey
> 
> P.S. VerifyWrites part, on the other hand, enforces very strong tospace
> invariant, and thus look salvageable if we somehow manage to accept fwdptr writes.
>