Adds a fragment-size= option to volume.config (#11865)

* Adds a fragment-size= option to volume.config

* Fix docstring

doc/admin-guide/files/volume.config.en.rst

@@ -76,6 +76,17 @@ line. This overrides the global :ts:cv:`proxy.config.cache.min_average_object_si
 configuration for this volume. This is useful if you have a volume that is dedicated
 for say very small objects, and you need a lot of directory entries to store them.
 
+Optional fragment size setting
+------------------------------
+
+You can also add an option ``fragment_size=<size>`` to the volume configuration
+line. This overrides the global :ts:cv:`proxy.config.cache.target_fragment_size`
+configuration for this volume. This allows for a smaller, or larger, fragment size
+for a particular volume. This may be useful together with ``avg_obj_size`` as well,
+since a larger fragment size could reduce the number of directory entries needed
+for a large object.
+
+Note that this setting has a maximmum value of 4MB.
 
 Exclusive spans and volume sizes
 ================================
@@ -116,4 +127,4 @@ ramcache has been disabled.::
     volume=2 scheme=http size=20%
     volume=3 scheme=http size=20%
     volume=4 scheme=http size=20% avg_obj_size=4096
-    volume=5 scheme=http size=20% ramcache=false
+    volume=5 scheme=http size=20% ramcache=false fragment_size=524288

src/iocore/cache/Cache.cc

@@ -273,7 +273,7 @@ Cache::open(bool clear, bool /* fix ATS_UNUSED */)
           for (; q; q = q->link.next) {
             blocks                         = q->b->len;
             CacheDisk *d                   = cp->disk_stripes[i]->disk;
-            cp->stripes[vol_no]            = new StripeSM(d, blocks, q->b->offset, cp->avg_obj_size);
+            cp->stripes[vol_no]            = new StripeSM(d, blocks, q->b->offset, cp->avg_obj_size, cp->fragment_size);
             cp->stripes[vol_no]->cache     = this;
             cp->stripes[vol_no]->cache_vol = cp;
 

src/iocore/cache/CacheHosting.cc

@@ -655,6 +655,7 @@ ConfigVolumes::BuildListFromString(char *config_file_path, char *file_buf)
     int         in_percent       = 0;
     bool        ramcache_enabled = true;
     int         avg_obj_size     = -1; // Defaults
+    int         fragment_size    = -1;
 
     while (true) {
       // skip all blank spaces at beginning of line
@@ -746,6 +747,13 @@ ConfigVolumes::BuildListFromString(char *config_file_path, char *file_buf)
         tmp          += 13;
         avg_obj_size  = atoi(tmp);
 
+        while (ParseRules::is_digit(*tmp)) {
+          tmp++;
+        }
+      } else if (strcasecmp(tmp, "fragment_size") == 0) { // match fragment_size
+        tmp           += 14;
+        fragment_size  = atoi(tmp);
+
         while (ParseRules::is_digit(*tmp)) {
           tmp++;
         }
@@ -786,6 +794,7 @@ ConfigVolumes::BuildListFromString(char *config_file_path, char *file_buf)
       configp->scheme           = scheme;
       configp->size             = size;
       configp->avg_obj_size     = avg_obj_size;
+      configp->fragment_size    = fragment_size;
       configp->cachep           = nullptr;
       configp->ramcache_enabled = ramcache_enabled;
       cp_queue.enqueue(configp);

src/iocore/cache/CacheProcessor.cc

@@ -1178,6 +1178,7 @@ cplist_update()
         if (cp->scheme == config_vol->scheme) {
           cp->ramcache_enabled = config_vol->ramcache_enabled;
           cp->avg_obj_size     = config_vol->avg_obj_size;
+          cp->fragment_size    = config_vol->fragment_size;
           config_vol->cachep   = cp;
         } else {
           /* delete this volume from all the disks */

src/iocore/cache/CacheWrite.cc

@@ -525,9 +525,10 @@ CacheVC::openWriteWriteDone(int event, Event *e)
 }
 
 static inline int
-target_fragment_size()
+target_fragment_size(int target_frag_size)
 {
-  uint64_t value = cache_config_target_fragment_size - sizeof(Doc);
+  uint64_t value = (target_frag_size > 0 ? target_frag_size : cache_config_target_fragment_size) - sizeof(Doc);
+
   ink_release_assert(value <= MAX_FRAG_SIZE);
   return value;
 }
@@ -561,6 +562,8 @@ CacheVC::openWriteMain(int /* event ATS_UNUSED */, Event * /* e ATS_UNUSED */)
   int64_t total_avail = vio.get_reader()->read_avail();
   int64_t avail       = total_avail;
   int64_t towrite     = avail + length;
+  int     frag_size   = target_fragment_size(stripe->frag_size);
+
   if (towrite > ntodo) {
     avail   -= (towrite - ntodo);
     towrite  = ntodo;
@@ -579,12 +582,12 @@ CacheVC::openWriteMain(int /* event ATS_UNUSED */, Event * /* e ATS_UNUSED */)
     total_len += avail;
   }
   length = static_cast<uint64_t>(towrite);
-  if (length > target_fragment_size() && (length < target_fragment_size() + target_fragment_size() / 4)) {
-    write_len = target_fragment_size();
+  if (length > frag_size && (length < frag_size + frag_size / 4)) {
+    write_len = frag_size;
   } else {
     write_len = length;
   }
-  bool not_writing = towrite != ntodo && towrite < target_fragment_size();
+  bool not_writing = towrite != ntodo && towrite < frag_size;
   if (!called_user) {
     if (not_writing) {
       called_user = 1;

src/iocore/cache/P_CacheHosting.h

@@ -297,6 +297,7 @@ struct ConfigVol {
   bool      ramcache_enabled;
   int       percent;
   int       avg_obj_size;
+  int       fragment_size;
   CacheVol *cachep;
   LINK(ConfigVol, link);
 };

src/iocore/cache/Stripe.cc

@@ -84,9 +84,10 @@ struct StripeInitInfo {
 // Stripe
 //
 
-Stripe::Stripe(CacheDisk *disk, off_t blocks, off_t dir_skip, int avg_obj_size)
+Stripe::Stripe(CacheDisk *disk, off_t blocks, off_t dir_skip, int avg_obj_size, int fragment_size)
   : path{ats_strdup(disk->path)},
     fd{disk->fd},
+    frag_size{fragment_size},
     skip{ROUND_TO_STORE_BLOCK((dir_skip < START_POS ? START_POS : dir_skip))},
     start{skip},
     len{blocks * STORE_BLOCK_SIZE},

src/iocore/cache/Stripe.h

@@ -52,6 +52,7 @@ struct CacheVol {
   off_t        size             = 0;
   int          num_vols         = 0;
   int          avg_obj_size     = -1; // Defer to the records.config if not overriden
+  int          fragment_size    = -1; // Defer to the records.config if not overriden
   bool         ramcache_enabled = true;
   StripeSM   **stripes          = nullptr;
   DiskStripe **disk_stripes     = nullptr;
@@ -86,6 +87,7 @@ class Stripe
   ats_scoped_str hash_text;
   char          *path = nullptr;
   int            fd{-1};
+  int            frag_size{-1};
 
   char                *raw_dir{nullptr};
   Dir                 *dir{};
@@ -115,7 +117,7 @@ class Stripe
    *
    * @see START_POS
    */
-  Stripe(CacheDisk *disk, off_t blocks, off_t dir_skip, int avg_obj_size = -1);
+  Stripe(CacheDisk *disk, off_t blocks, off_t dir_skip, int avg_obj_size = -1, int fragment_size = -1);
 
   int dir_check();
 

src/iocore/cache/StripeSM.cc

@@ -112,8 +112,10 @@ struct StripeInitInfo {
 // This is weird: the len passed to the constructor for _preserved_dirs is
 // initialized in the superclasse's constructor. This is safe because the
 // superclass should always be initialized first.
-StripeSM::StripeSM(CacheDisk *disk, off_t blocks, off_t dir_skip, int avg_obj_size)
-  : Continuation(new_ProxyMutex()), Stripe{disk, blocks, dir_skip, avg_obj_size}, _preserved_dirs{static_cast<int>(len)}
+StripeSM::StripeSM(CacheDisk *disk, off_t blocks, off_t dir_skip, int avg_obj_size, int fragment_size)
+  : Continuation(new_ProxyMutex()),
+    Stripe{disk, blocks, dir_skip, avg_obj_size, fragment_size},
+    _preserved_dirs{static_cast<int>(len)}
 {
   open_dir.mutex = this->mutex;
   SET_HANDLER(&StripeSM::aggWrite);

src/iocore/cache/StripeSM.h

@@ -165,10 +165,14 @@ class StripeSM : public Continuation, public Stripe
    * @param blocks: Number of blocks. Must be at least 10.
    * @param dir_skip: Offset into the disk at which to start the stripe.
    * If this value is less than START_POS, START_POS will be used instead.
+   * @param avg_obj_size: Optional average object size. If not provided, use default
+   * from proxy.config.cache.min_average_object_size.
+   * @param fragment_size: Optional fragment size. If not provided, use default
+   * from proxy.config.cache.target_fragment_size.
    *
    * @see START_POS
    */
-  StripeSM(CacheDisk *disk, off_t blocks, off_t dir_skip, int avg_obj_size = -1);
+  StripeSM(CacheDisk *disk, off_t blocks, off_t dir_skip, int avg_obj_size = -1, int fragment_size = -1);
 
   Queue<CacheVC, Continuation::Link_link> &get_pending_writers();