From 60bb8b1453e2f93d13e7bb44e8e46c085d2dd752 Mon Sep 17 00:00:00 2001 From: "Shawn O. Pearce" Date: Sat, 23 Dec 2006 02:34:28 -0500 Subject: Fully activate the sliding window pack access. This finally turns on the sliding window behavior for packfile data access by mapping limited size windows and chaining them under the packed_git->windows list. We consider a given byte offset to be within the window only if there would be at least 20 bytes (one hash worth of data) accessible after the requested offset. This range selection relates to the contract that use_pack() makes with its callers, allowing them to access one hash or one object header without needing to call use_pack() for every byte of data obtained. In the worst case scenario we will map the same page of data twice into memory: once at the end of one window and once again at the start of the next window. This duplicate page mapping will happen only when an object header or a delta base reference is spanned over the end of a window and is always limited to just one page of duplication, as no sane operating system will ever have a page size smaller than a hash. I am assuming that the possible wasted page of virtual address space is going to perform faster than the alternatives, which would be to copy the object header or ref delta into a temporary buffer prior to parsing, or to check the window range on every byte during header parsing. We may decide to revisit this decision in the future since this is just a gut instinct decision and has not actually been proven out by experimental testing. Signed-off-by: Shawn O. Pearce Signed-off-by: Junio C Hamano --- cache.h | 1 + 1 file changed, 1 insertion(+) (limited to 'cache.h') diff --git a/cache.h b/cache.h index c927f29d31..c7d7e4dcc0 100644 --- 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_window_size; extern size_t packed_git_limit; #define GIT_REPO_VERSION 0 -- cgit v1.2.3