216 lines
7.6 KiB
Diff
216 lines
7.6 KiB
Diff
Upstream-Status: Backport
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unsquashfs: fix open file limit
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Previously Unsquashfs relied on the to_writer queue being
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set to 1000 to limit the amount of open file read-ahead to a
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maximum of 500. For the default process limit of 1024 open files
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this was perhaps acceptable, but it obviously breaks if ulimit has
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been used to set the open file limit to below 504 (this includes
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stdin, stdout, stderr and the Squashfs filesystem being unsquashed).
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More importantly setting the to_writer queue to 1000 to limit
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the amount of files open has always been an inherent performance
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hit because the to_writer queue queues blocks. It limits the
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block readhead to 1000 blocks, irrespective of how many files
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that represents. A single file containing more than 1000 blocks
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will still be limited to a 1000 block readahead even though the
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data block cache typically can buffer more than this (at the
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default data cache size of 256 Mbytes and the default block size
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of 128 Kbytes, it can buffer 2048 blocks). Obviously the
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caches serve more than just a read-ahead role (they also
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cache decompressed blocks in case they're referenced later e.g.
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by duplicate files), but the artificial limit imposed on
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the read-ahead due to setting the to_writer queue to 1000 is
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unnecessary.
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This commit does away with the need to limit the to_writer queue,
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by introducing open_wait() and close_wake() calls which correctly
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track the amount of open files.
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Signed-off-by: Phillip Lougher <phillip@squashfs.org.uk>
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Signed-off-by: yanjun.zhu <yanjun.zhu@windriver.com>
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diff -urpN a/unsquashfs.c b/unsquashfs.c
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--- a/unsquashfs.c 2012-11-30 15:31:29.000000000 +0800
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+++ b/unsquashfs.c 2012-11-30 15:32:03.000000000 +0800
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@@ -31,6 +31,8 @@
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#include <sys/sysinfo.h>
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#include <sys/types.h>
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+#include <sys/time.h>
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+#include <sys/resource.h>
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struct cache *fragment_cache, *data_cache;
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struct queue *to_reader, *to_deflate, *to_writer, *from_writer;
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@@ -784,6 +786,46 @@ failure:
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}
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+pthread_mutex_t open_mutex = PTHREAD_MUTEX_INITIALIZER;
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+pthread_cond_t open_empty = PTHREAD_COND_INITIALIZER;
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+int open_unlimited, open_count;
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+#define OPEN_FILE_MARGIN 10
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+
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+
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+void open_init(int count)
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+{
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+ open_count = count;
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+ open_unlimited = count == -1;
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+}
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+
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+
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+int open_wait(char *pathname, int flags, mode_t mode)
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+{
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+ if (!open_unlimited) {
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+ pthread_mutex_lock(&open_mutex);
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+ while (open_count == 0)
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+ pthread_cond_wait(&open_empty, &open_mutex);
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+ open_count --;
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+ pthread_mutex_unlock(&open_mutex);
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+ }
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+
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+ return open(pathname, flags, mode);
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+}
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+
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+
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+void close_wake(int fd)
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+{
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+ close(fd);
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+
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+ if (!open_unlimited) {
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+ pthread_mutex_lock(&open_mutex);
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+ open_count ++;
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+ pthread_cond_signal(&open_empty);
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+ pthread_mutex_unlock(&open_mutex);
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+ }
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+}
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+
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+
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int write_file(struct inode *inode, char *pathname)
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{
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unsigned int file_fd, i;
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@@ -794,8 +836,8 @@ int write_file(struct inode *inode, char
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TRACE("write_file: regular file, blocks %d\n", inode->blocks);
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- file_fd = open(pathname, O_CREAT | O_WRONLY | (force ? O_TRUNC : 0),
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- (mode_t) inode->mode & 0777);
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+ file_fd = open_wait(pathname, O_CREAT | O_WRONLY |
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+ (force ? O_TRUNC : 0), (mode_t) inode->mode & 0777);
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if(file_fd == -1) {
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ERROR("write_file: failed to create file %s, because %s\n",
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pathname, strerror(errno));
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@@ -1712,7 +1754,7 @@ void *writer(void *arg)
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}
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}
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- close(file_fd);
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+ close_wake(file_fd);
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if(failed == FALSE)
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set_attributes(file->pathname, file->mode, file->uid,
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file->gid, file->time, file->xattr, force);
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@@ -1803,9 +1845,9 @@ void *progress_thread(void *arg)
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void initialise_threads(int fragment_buffer_size, int data_buffer_size)
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{
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- int i;
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+ struct rlimit rlim;
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+ int i, max_files, res;
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sigset_t sigmask, old_mask;
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- int all_buffers_size = fragment_buffer_size + data_buffer_size;
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sigemptyset(&sigmask);
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sigaddset(&sigmask, SIGINT);
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@@ -1841,10 +1883,86 @@ void initialise_threads(int fragment_buf
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EXIT_UNSQUASH("Out of memory allocating thread descriptors\n");
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deflator_thread = &thread[3];
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- to_reader = queue_init(all_buffers_size);
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- to_deflate = queue_init(all_buffers_size);
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- to_writer = queue_init(1000);
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+ /*
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+ * dimensioning the to_reader and to_deflate queues. The size of
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+ * these queues is directly related to the amount of block
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+ * read-ahead possible. To_reader queues block read requests to
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+ * the reader thread and to_deflate queues block decompression
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+ * requests to the deflate thread(s) (once the block has been read by
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+ * the reader thread). The amount of read-ahead is determined by
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+ * the combined size of the data_block and fragment caches which
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+ * determine the total number of blocks which can be "in flight"
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+ * at any one time (either being read or being decompressed)
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+ *
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+ * The maximum file open limit, however, affects the read-ahead
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+ * possible, in that for normal sizes of the fragment and data block
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+ * caches, where the incoming files have few data blocks or one fragment
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+ * only, the file open limit is likely to be reached before the
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+ * caches are full. This means the worst case sizing of the combined
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+ * sizes of the caches is unlikely to ever be necessary. However, is is
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+ * obvious read-ahead up to the data block cache size is always possible
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+ * irrespective of the file open limit, because a single file could
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+ * contain that number of blocks.
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+ *
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+ * Choosing the size as "file open limit + data block cache size" seems
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+ * to be a reasonable estimate. We can reasonably assume the maximum
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+ * likely read-ahead possible is data block cache size + one fragment
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+ * per open file.
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+ *
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+ * dimensioning the to_writer queue. The size of this queue is
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+ * directly related to the amount of block read-ahead possible.
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+ * However, unlike the to_reader and to_deflate queues, this is
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+ * complicated by the fact the to_writer queue not only contains
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+ * entries for fragments and data_blocks but it also contains
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+ * file entries, one per open file in the read-ahead.
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+ *
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+ * Choosing the size as "2 * (file open limit) +
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+ * data block cache size" seems to be a reasonable estimate.
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+ * We can reasonably assume the maximum likely read-ahead possible
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+ * is data block cache size + one fragment per open file, and then
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+ * we will have a file_entry for each open file.
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+ */
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+ res = getrlimit(RLIMIT_NOFILE, &rlim);
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+ if (res == -1) {
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+ ERROR("failed to get open file limit! Defaulting to 1\n");
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+ rlim.rlim_cur = 1;
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+ }
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+
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+ if (rlim.rlim_cur != RLIM_INFINITY) {
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+ /*
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+ * leave OPEN_FILE_MARGIN free (rlim_cur includes fds used by
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+ * stdin, stdout, stderr and filesystem fd
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+ */
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+ if (rlim.rlim_cur <= OPEN_FILE_MARGIN)
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+ /* no margin, use minimum possible */
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+ max_files = 1;
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+ else
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+ max_files = rlim.rlim_cur - OPEN_FILE_MARGIN;
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+ } else
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+ max_files = -1;
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+
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+ /* set amount of available files for use by open_wait and close_wake */
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+ open_init(max_files);
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+
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+ /*
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+ * allocate to_reader, to_deflate and to_writer queues. Set based on
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+ * open file limit and cache size, unless open file limit is unlimited,
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+ * in which case set purely based on cache limits
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+ */
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+ if (max_files != -1) {
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+ to_reader = queue_init(max_files + data_buffer_size);
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+ to_deflate = queue_init(max_files + data_buffer_size);
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+ to_writer = queue_init(max_files * 2 + data_buffer_size);
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+ } else {
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+ int all_buffers_size = fragment_buffer_size + data_buffer_size;
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+
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+ to_reader = queue_init(all_buffers_size);
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+ to_deflate = queue_init(all_buffers_size);
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+ to_writer = queue_init(all_buffers_size * 2);
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+ }
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+
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from_writer = queue_init(1);
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+
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fragment_cache = cache_init(block_size, fragment_buffer_size);
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data_cache = cache_init(block_size, data_buffer_size);
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pthread_create(&thread[0], NULL, reader, NULL);
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