Refactor packed_git to prepare for sliding mmap windows.

The idea behind the sliding mmap window pack reader implementation
is to have multiple mmap regions active against the same pack file,
thereby allowing the process to mmap in only the active/hot sections
of the pack and reduce overall virtual address space usage.

To implement this we need to refactor the mmap related data
(pack_base, pack_use_cnt) out of struct packed_git and move them
into a new struct pack_window.

We are refactoring the code to support a single struct pack_window
per packfile, thereby emulating the prior behavior of mmap'ing the
entire pack file.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>

1 files changed, 10 insertions, 3 deletions

diff --git a/cache.h b/cache.h
index 816239bea..ae7bceca5 100644
--- a/cache.h
+++ b/cache.h
@@ -336,14 +336,21 @@ extern struct alternate_object_database {
 } *alt_odb_list;
 extern void prepare_alt_odb(void);
 
+struct pack_window {
+	struct pack_window *next;
+	unsigned char *base;
+	off_t offset;
+	size_t len;
+	unsigned int last_used;
+	unsigned int inuse_cnt;
+};
+
 extern struct packed_git {
 	struct packed_git *next;
 	unsigned long index_size;
 	unsigned long pack_size;
+	struct pack_window *windows;
 	unsigned int *index_base;
-	void *pack_base;
-	unsigned int pack_last_used;
-	unsigned int pack_use_cnt;
 	int pack_local;
 	unsigned char sha1[20];
 	/* something like ".git/objects/pack/xxxxx.pack" */