Introduce new config option for mmap limit.

Rather than hardcoding the maximum number of bytes which can be
mmapped from pack files we should make this value configurable,
allowing the end user to increase or decrease this limit on a
per-repository basis depending on the size of the repository
and the capabilities of their operating system.

In general users should not need to manually tune such a low-level
setting within the core code, but being able to artifically limit
the number of bytes which we can mmap at once from pack files will
make it easier to craft test cases for the new mmap sliding window
implementation.

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

diff --git a/Documentation/config.txt b/Documentation/config.txt
index 178e0e1e209e066ad220d6ba95be0728c2db5e99..28fe6942cf867549e8d19120e339a14cb8347b1b 100644 (file)
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -118,6 +118,15 @@ core.legacyheaders::
        database directly (where the "http://" and "rsync://" protocols
        count as direct access).
 
+core.packedGitLimit::
+       Maximum number of bytes to map simultaneously into memory
+       from pack files.  If Git needs to access more than this many
+       bytes at once to complete an operation it will unmap existing
+       regions to reclaim virtual address space within the process.
+       Default is 256 MiB, which should be reasonable for all
+       users/operating systems, except on largest Git projects.
+       You probably do not need to adjust this value.
+
 alias.*::
        Command aliases for the gitlink:git[1] command wrapper - e.g.
        after defining "alias.last = cat-file commit HEAD", the invocation

diff --git a/cache.h b/cache.h
index e0a26e9d04857484f07bd49f740e653085129447..816239bea0fbf53852efcb3575995cd5aef7e445 100644 (file)
--- a/cache.h
+++ b/cache.h
@@ -196,6 +196,7 @@ extern int warn_ambiguous_refs;
 extern int shared_repository;
 extern const char *apply_default_whitespace;
 extern int zlib_compression_level;
+extern size_t packed_git_limit;
 
 #define GIT_REPO_VERSION 0
 extern int repository_format_version;

diff --git a/config.c b/config.c
index fcccf7e2a4f3b7487af10d4f7b505c7ef492b9e8..0c21286cb25d6a0d1f4dca4e82e59dcb7165e0d5 100644 (file)
--- a/config.c
+++ b/config.c
@@ -298,6 +298,11 @@ int git_default_config(const char *var, const char *value)
                return 0;
        }
 
+       if (!strcmp(var, "core.packedgitlimit")) {
+               packed_git_limit = git_config_int(var, value);
+               return 0;
+       }
+
        if (!strcmp(var, "user.name")) {
                strlcpy(git_default_name, value, sizeof(git_default_name));
                return 0;

diff --git a/environment.c b/environment.c
index a1502c4e87c0067c8cc276006317005a0da21a49..a3ddae68a7bada16edfa88d8f9244181af8e7cea 100644 (file)
--- a/environment.c
+++ b/environment.c
@@ -23,6 +23,7 @@ char *git_log_output_encoding;
 int shared_repository = PERM_UMASK;
 const char *apply_default_whitespace;
 int zlib_compression_level = Z_DEFAULT_COMPRESSION;
+size_t packed_git_limit = 256 * 1024 * 1024;
 int pager_in_use;
 int pager_use_color = 1;
 

diff --git a/sha1_file.c b/sha1_file.c
index 4824a5d4d8bb5104461ea8245d9a22b5408cb537..4183f595edfe6086f5097a430cb48202db00c5c1 100644 (file)
--- a/sha1_file.c
+++ b/sha1_file.c
@@ -397,7 +397,6 @@ static char *find_sha1_file(const unsigned char *sha1, struct stat *st)
        return NULL;
 }
 
-#define PACK_MAX_SZ (1<<26)
 static int pack_used_ctr;
 static unsigned long pack_mapped;
 struct packed_git *packed_git;
@@ -490,7 +489,7 @@ int use_packed_git(struct packed_git *p)
                struct pack_header *hdr;
 
                pack_mapped += p->pack_size;
-               while (PACK_MAX_SZ < pack_mapped && unuse_one_packed_git())
+               while (packed_git_limit < pack_mapped && unuse_one_packed_git())
                        ; /* nothing */
                fd = open(p->pack_name, O_RDONLY);
                if (fd < 0)