stef...@apache.org wrote on Wed, Oct 27, 2010 at 20:47:06 -0000: > Author: stefan2 > Date: Wed Oct 27 20:47:06 2010 > New Revision: 1028094 > > URL: http://svn.apache.org/viewvc?rev=1028094&view=rev > Log: > If we allocate stringbufs, their actual capacity allocated by APR > is often larger than requested. Take advantage of that by requesting > an enlarged buffer in the first place. Especially for short or empty > strings, this saves some re-allocations once they grow. > > * subversion/libsvn_subr/svn_string.c > (svn_stringbuf_ncreate): allocate a buffer of aligned size > > Modified: > subversion/branches/performance/subversion/libsvn_subr/svn_string.c > > Modified: subversion/branches/performance/subversion/libsvn_subr/svn_string.c > URL: > http://svn.apache.org/viewvc/subversion/branches/performance/subversion/libsvn_subr/svn_string.c?rev=1028094&r1=1028093&r2=1028094&view=diff > ============================================================================== > --- subversion/branches/performance/subversion/libsvn_subr/svn_string.c > (original) > +++ subversion/branches/performance/subversion/libsvn_subr/svn_string.c Wed > Oct 27 20:47:06 2010 > @@ -266,9 +266,21 @@ svn_stringbuf_create_ensure(apr_size_t b > svn_stringbuf_t * > svn_stringbuf_ncreate(const char *bytes, apr_size_t size, apr_pool_t *pool) > { > - /* Ensure string buffer of size + 1 */ > - svn_stringbuf_t *strbuf = svn_stringbuf_create_ensure(size, pool); > + char *data; >
Is this new variable used anywhere? > + /* apr_palloc will allocate multiples of 8. > + * Thus, we would waste some of that memory if we stuck to the > + * smaller size. Note that this is safe even if apr_palloc would > + * use some other aligment or none at all. */ > + apr_size_t aligned_size = APR_ALIGN_DEFAULT(size + 1) - 1; > + So, this rounds the requested number of bytes (size+1) to the next multiple of 8, then subtracts 1 from the result? Net effect being that if we need 1 byte, we get 7; and if we need 2 or 7 bytes, then we get 7 bytes, right? But if we need size+1=8 bytes, then.. I think we get aligned_size=7, and svn_stringbuf_create_ensure() compensates because it allocates one byte more than requested, right? > + /* Ensure string buffer of aligned_size + 1. > + * This should allocate the same amount of memory as "size" would. */ > + svn_stringbuf_t *strbuf = svn_stringbuf_create_ensure(aligned_size, pool); > + Could this "use aligned_size instead of size" logic be pushed down to svn_stringbuf_create_ensure()? > + /* Actually, aligned_size+1 would be faster but we cannot be entirely > + * sure that the source string has been aligned properly such that > + * all the extra bytes would actually come from addressible memory.*/ > memcpy(strbuf->data, bytes, size); > > /* Null termination is the convention -- even if we suspect the data > >
