From 00727249ec8404c68391ec58e9c9f0d8a88d5ca0 Mon Sep 17 00:00:00 2001 From: Paulo Casaretto Date: Fri, 29 Aug 2025 16:02:54 +0000 Subject: range-diff: add configurable memory limit for cost matrix MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit When comparing large commit ranges (e.g., 250,000+ commits), range-diff attempts to allocate an n×n cost matrix that can exhaust available memory. For example, with 256,784 commits (n = 513,568), the matrix would require approximately 256GB of memory (513,568² × 4 bytes), causing either immediate segmentation faults due to integer overflow or system hangs. Add a memory limit check in get_correspondences() before allocating the cost matrix. This check uses the total size in bytes (n² × sizeof(int)) and compares it against a configurable maximum, preventing both excessive memory usage and integer overflow issues. The limit is configurable via a new --max-memory option that accepts human-readable sizes (e.g., "1G", "500M"). The default is 4GB for 64 bit systems and 2GB for 32 bit systems. This allows comparing ranges of approximately 32,000 (16,000) commits - generous for real-world use cases while preventing impractical operations. When the limit is exceeded, range-diff now displays a clear error message showing both the requested memory size and the maximum allowed, formatted in human-readable units for better user experience. Example usage: git range-diff --max-memory=1G branch1...branch2 git range-diff --max-memory=500M base..topic1 base..topic2 This approach was chosen over alternatives: - Pre-counting commits: Would require spawning additional git processes and reading all commits twice - Limiting by commit count: Less precise than actual memory usage - Streaming approach: Would require significant refactoring of the current algorithm This issue was previously discussed in: https://lore.kernel.org/git/RFC-cover-v2-0.5-00000000000-20211210T122901Z-avarab@gmail.com/ Acked-by: Johannes Schindelin Signed-off-by: Paulo Casaretto Signed-off-by: Junio C Hamano --- range-diff.h | 5 +++++ 1 file changed, 5 insertions(+) (limited to 'range-diff.h') diff --git a/range-diff.h b/range-diff.h index cd85000b5a..9d39818e34 100644 --- a/range-diff.h +++ b/range-diff.h @@ -5,6 +5,10 @@ #include "strvec.h" #define RANGE_DIFF_CREATION_FACTOR_DEFAULT 60 +#define RANGE_DIFF_MAX_MEMORY_DEFAULT \ + (sizeof(void*) >= 8 ? \ + ((size_t)(1024L * 1024L) * (size_t)(4L * 1024L)) : /* 4GB on 64-bit */ \ + ((size_t)(1024L * 1024L) * (size_t)(2L * 1024L))) /* 2GB on 32-bit */ /* * A much higher value than the default, when we KNOW we are comparing @@ -17,6 +21,7 @@ struct range_diff_options { unsigned dual_color:1; unsigned left_only:1, right_only:1; unsigned include_merges:1; + size_t max_memory; const struct diff_options *diffopt; /* may be NULL */ const struct strvec *other_arg; /* may be NULL */ }; -- cgit v1.2.3