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[core] chunkqueue_peek_data() mmap experiment

chunkqueue_peek_data() experiment to mmap temporary files

(currently disabled in code due to not making measurable difference
 in throughput (during a specific microbenchmark load test),
 though it does reduce CPU use by ~10% in the same microbenchmark)

enabling this may cause large spikes in RSS mem usage reported by the
system, due to the read-only memory maps of the temporary files,
but this is nothing to be alarmed about, as the memory maps are
file-backed and read-only, so minimally add to memory pressure
master
Glenn Strauss 2 months ago
parent
commit
23fe1312e5
  1. 36
      src/chunk.c

36
src/chunk.c

@ -1444,6 +1444,42 @@ chunkqueue_peek_data (chunkqueue * const cq,
if (0 == len)
break;
#if 0 /* XXX: might improve performance on some system workloads */
#if defined(_LP64) || defined(__LP64__) || defined(_WIN64)
#if defined(HAVE_MMAP) || defined(_WIN32) /*see local sys-mmap.h*/
/* mmap file to access data
* (Only consider temp files here since not catching SIGBUS)
* (For now, also limit to 64-bit to avoid address space issues)
* If temp file is used, data should be large enough that mmap
* is worthwhile. fd need not be kept open for the mmap once
* the mmap has been created, but is currently kept open for
* other pre-existing logic which checks fd and opens file,
* such as the condition for entering this code block above. */
/* Note: under heavy load (or microbenchmark), system-reported
* memory use for RSS can be very, very large, due to presence
* of lots and lots of temp file read-only memory maps.
* pmap -X and exclude lighttpd temporary files to get a better
* view of memory use */
char *mdata;
if (c->file.is_temp
&& (mdata = chunkqueue_mmap_chunk_len(c, len))) {
if (*dlen) {
if (*data != data_in) {
memcpy(data_in, *data, *dlen);
*data = data_in;
}
memcpy(data_in+*dlen, mdata, (size_t)len);
}
else {
*data = mdata;
}
*dlen += (uint32_t)len;
break;
}
#endif
#endif
#endif
#ifndef HAVE_PREAD
if (-1 == lseek(c->file.fd, offset, SEEK_SET)) {
log_perror(errh, __FILE__, __LINE__, "lseek(\"%s\")",

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