• ggaren@apple.com's avatar
    Code cache should be explicit about what it caches · 818f283e
    ggaren@apple.com authored
    https://bugs.webkit.org/show_bug.cgi?id=110039
    
    Reviewed by Oliver Hunt.
    
    This patch makes the code cache more explicit in two ways:
    
    (1) The cache caches top-level scripts. Any sub-functions executed as a
    part of a script are cached with it and evicted with it.
    
    This simplifies things by eliminating out-of-band sub-function tracking,
    and fixes pathological cases where functions for live scripts would be
    evicted in favor of functions for dead scripts, and/or high probability
    functions executed early in script lifetime would be evicted in favor of
    low probability functions executed late in script lifetime, due to LRU.
    
    Statistical data from general browsing and PLT confirms that caching
    functions independently of scripts is not profitable.
    
    (2) The cache tracks script size, not script count.
    
    This reduces the worst-case cache size by a factor of infinity.
    
    Script size is a reasonable first-order estimate of in-memory footprint 
    for a cached script because there are no syntactic constructs that have
    super-linear memory footprint.
    
    * bytecode/UnlinkedCodeBlock.cpp:
    (JSC::generateFunctionCodeBlock): Moved this function out of the cache
    because it does not consult the cache, and is not managed by it.
    
    (JSC::UnlinkedFunctionExecutable::visitChildren): Visit our code blocks
    because they are strong references now, rather than weak, a la (1).
    
    (JSC::UnlinkedFunctionExecutable::codeBlockFor): Updated for interface changes.
    
    * bytecode/UnlinkedCodeBlock.h:
    (UnlinkedFunctionExecutable):
    (UnlinkedFunctionCodeBlock): Strong now, not weak, a la (1).
    
    * runtime/CodeCache.cpp:
    (JSC::CodeCache::CodeCache):
    * runtime/CodeCache.h:
    (JSC::SourceCodeKey::length):
    (SourceCodeKey):
    (CodeCacheMap):
    (JSC::CodeCacheMap::CodeCacheMap):
    (JSC::CodeCacheMap::find):
    (JSC::CodeCacheMap::set):
    (JSC::CodeCacheMap::clear):
    (CodeCache):
    (JSC::CodeCache::clear): Removed individual function tracking, due to (1).
    Added explicit character counting, for (2).
    
    You might think 16000000 characters is a lot. It is. But this patch
    didn't establish that limit -- it just took the existing limit and
    made it more visible. I intend to reduce the size of the cache in a
    future patch.
    
    
    git-svn-id: http://svn.webkit.org/repository/webkit/trunk@143133 268f45cc-cd09-0410-ab3c-d52691b4dbfc
    818f283e
CodeCache.cpp 6.27 KB