sha1_file: introduce close_one_pack() to close packs on fd pressure

diff --git a/sha1_file.c b/sha1_file.c
index 40b23297b2e1e60a3719e9c67256303e39456604..263cf71c27fa81f60da5a8688d899b66b1967d23 100644 (file)
--- a/sha1_file.c
+++ b/sha1_file.c
@@ -673,6 +673,83 @@ void close_pack_windows(struct packed_git *p)
        }
 }
 
+/*
+ * The LRU pack is the one with the oldest MRU window, preferring packs
+ * with no used windows, or the oldest mtime if it has no windows allocated.
+ */
+static void find_lru_pack(struct packed_git *p, struct packed_git **lru_p, struct pack_window **mru_w, int *accept_windows_inuse)
+{
+       struct pack_window *w, *this_mru_w;
+       int has_windows_inuse = 0;
+
+       /*
+        * Reject this pack if it has windows and the previously selected
+        * one does not.  If this pack does not have windows, reject
+        * it if the pack file is newer than the previously selected one.
+        */
+       if (*lru_p && !*mru_w && (p->windows || p->mtime > (*lru_p)->mtime))
+               return;
+
+       for (w = this_mru_w = p->windows; w; w = w->next) {
+               /*
+                * Reject this pack if any of its windows are in use,
+                * but the previously selected pack did not have any
+                * inuse windows.  Otherwise, record that this pack
+                * has windows in use.
+                */
+               if (w->inuse_cnt) {
+                       if (*accept_windows_inuse)
+                               has_windows_inuse = 1;
+                       else
+                               return;
+               }
+
+               if (w->last_used > this_mru_w->last_used)
+                       this_mru_w = w;
+
+               /*
+                * Reject this pack if it has windows that have been
+                * used more recently than the previously selected pack.
+                * If the previously selected pack had windows inuse and
+                * we have not encountered a window in this pack that is
+                * inuse, skip this check since we prefer a pack with no
+                * inuse windows to one that has inuse windows.
+                */
+               if (*mru_w && *accept_windows_inuse == has_windows_inuse &&
+                   this_mru_w->last_used > (*mru_w)->last_used)
+                       return;
+       }
+
+       /*
+        * Select this pack.
+        */
+       *mru_w = this_mru_w;
+       *lru_p = p;
+       *accept_windows_inuse = has_windows_inuse;
+}
+
+static int close_one_pack(void)
+{
+       struct packed_git *p, *lru_p = NULL;
+       struct pack_window *mru_w = NULL;
+       int accept_windows_inuse = 1;
+
+       for (p = packed_git; p; p = p->next) {
+               if (p->pack_fd == -1)
+                       continue;
+               find_lru_pack(p, &lru_p, &mru_w, &accept_windows_inuse);
+       }
+
+       if (lru_p) {
+               close(lru_p->pack_fd);
+               pack_open_fds--;
+               lru_p->pack_fd = -1;
+               return 1;
+       }
+
+       return 0;
+}
+
 void unuse_pack(struct pack_window **w_cursor)
 {
        struct pack_window *w = *w_cursor;
@@ -768,7 +845,7 @@ static int open_packed_git_1(struct packed_git *p)
                        pack_max_fds = 1;
        }
 
-       while (pack_max_fds <= pack_open_fds && unuse_one_window(NULL, -1))
+       while (pack_max_fds <= pack_open_fds && close_one_pack())
                ; /* nothing */
 
        p->pack_fd = git_open_noatime(p->pack_name);