Bug 98084 – Block freeing thread should sleep indefinitely when there's no work to do

• Status: RESOLVED
• Resolution: FIXED
• Component: JavaScriptCore

[Mark Hahnenberg]

Current the block freeing thread wakes up once a second to check if there are any blocks for it to release back to the OS. This is wasteful. We should change it to sleep when it realizes there are no more blocks to free. Any thread that returns a block to the BlockAllocator should then notify the block freeing thread that there is more work to do now.

[Mark Hahnenberg]

Created attachment 166562 [details]
Patch

[Geoffrey Garen]

Comment on attachment 166562 [details]
Patch

View in context: https://bugs.webkit.org/attachment.cgi?id=166562&action=review

This fix looks correct, but I think it can get better.

> Source/JavaScriptCore/heap/BlockAllocator.h:111
> +        m_numberOfFreeBlocks++;

Can we just use m_numberOfFreeBlocks != 0, instead of a separate m_blocksNeedFreeing boolean, to tell if we need to free anything?

> Source/JavaScriptCore/heap/BlockAllocator.h:118
> +    MutexLocker mutexLocker(m_freeBlockConditionLock);
> +    if (!m_blocksNeedFreeing) {
> +        m_blocksNeedFreeing = true;
> +        m_freeBlockCondition.signal();
> +    }

Rather than doing this unconditionally, I'd prefer to see this done only if m_numberOfFreeBlocks was 0 when we acquired the lock.

[Mark Hahnenberg]

Created attachment 166587 [details]
Patch

[Geoffrey Garen]

Comment on attachment 166587 [details]
Patch

View in context: https://bugs.webkit.org/attachment.cgi?id=166587&action=review

r=me

> Source/JavaScriptCore/heap/BlockAllocator.h:115
> +    MutexLocker mutexLocker(m_freeBlockConditionLock);
> +    if (!numberOfFreeBlocks)

"mutexLocker" should be scoped inside "if (!numberOfFreeBlocks)", so we only acquire the mutex on the transition from zero to non-zero. Please make this change before landing.

[Mark Hahnenberg]

Committed r130212: <http://trac.webkit.org/changeset/130212>

[Mark Hahnenberg]

<rdar://problem/12350667>

[Yong Li]

*** Bug 90622 has been marked as a duplicate of this bug. ***

[Mark Hahnenberg]

Reopening because this wasn't completely fixed.

[Mark Hahnenberg]

Created attachment 169199 [details]
Patch

[Geoffrey Garen]

Comment on attachment 169199 [details]
Patch

r=me

[WebKit Review Bot]

Comment on attachment 169199 [details]
Patch

Clearing flags on attachment: 169199

Committed r131619: <http://trac.webkit.org/changeset/131619>

[WebKit Review Bot]

All reviewed patches have been landed.  Closing bug.