[PATCH v4] convert: avoid high memory footprint

["Haritha via GitGitGadget" <gitgitgadget@gmail.com>]

From: D Harithamma <harithamma.d@ibm.com>

When Git adds a file requiring encoding conversion and tracing of encoding
conversion is not requested via the GIT_TRACE_WORKING_TREE_ENCODING
environment variable, the `trace_encoding()` function still allocates &
prepares "human readable" copies of the file contents before and after
conversion to show in the trace. This results in a high memory footprint
and increased runtime without providing any user-visible benefit.

This fix introduces an early exit from the `trace_encoding()` function
when tracing is not requested, preventing unnecessary memory allocation
and processing.

Signed-off-by: Harithamma D <harithamma.d@ibm.com>
---
    Fix to avoid high memory footprint
    
    This fix avoids high memory footprint when adding files that require
    conversion
    
    Git has a trace_encoding routine that prints trace output when
    GIT_TRACE_WORKING_TREE_ENCODING=1 is set. This environment variable is
    used to debug the encoding contents. When a 40MB file is added, it
    requests close to 1.8GB of storage from xrealloc which can lead to out
    of memory errors. However, the check for GIT_TRACE_WORKING_TREE_ENCODING
    is done after the string is allocated. This resolves high memory
    footprints even when GIT_TRACE_WORKING_TREE_ENCODING is not active. This
    fix adds an early exit to avoid the unnecessary memory allocation.

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-1744%2FHarithaIBM%2FmemFootprintFix-v4
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-1744/HarithaIBM/memFootprintFix-v4
Pull-Request: https://github.com/git/git/pull/1744

Range-diff vs v3:

 1:  d864de64380 ! 1:  50758a4fb94 Fix to avoid high memory footprint
     @@ Metadata
      Author: D Harithamma <harithamma.d@ibm.com>
      
       ## Commit message ##
     -    Fix to avoid high memory footprint
     +    convert: avoid high memory footprint
      
          When Git adds a file requiring encoding conversion and tracing of encoding
          conversion is not requested via the GIT_TRACE_WORKING_TREE_ENCODING


 convert.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/convert.c b/convert.c
index d8737fe0f2d..c4ddc4de81b 100644
--- a/convert.c
+++ b/convert.c
@@ -324,6 +324,9 @@ static void trace_encoding(const char *context, const char *path,
 	struct strbuf trace = STRBUF_INIT;
 	int i;
 
+	if (!trace_want(&coe))
+		return;
+
 	strbuf_addf(&trace, "%s (%s, considered %s):\n", context, path, encoding);
 	for (i = 0; i < len && buf; ++i) {
 		strbuf_addf(

base-commit: 557ae147e6cdc9db121269b058c757ac5092f9c9
-- 
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