[dpkg] 43/200: libdpkg: Only preallocate disk size for files bigger than 16 KiB

[Ximin Luo]

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commit a971ad91437af8880cad4703695dcf12ee45959b
Author: Guillem Jover <guillem at debian.org>
Date:   Wed Nov 16 03:00:07 2016 +0100

    libdpkg: Only preallocate disk size for files bigger than 16 KiB
    
    Preallocating for very small fails causes some filesystems to degrade
    performance. Do so only for "big enough" files.
    
    Closes: #824636
---
 debian/changelog | 2 ++
 lib/dpkg/fdio.c  | 4 +++-
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/debian/changelog b/debian/changelog
index 5a8f8ba..78a3b48 100644
--- a/debian/changelog
+++ b/debian/changelog
@@ -15,6 +15,8 @@ dpkg (1.18.15) UNRELEASED; urgency=medium
     execution when we cannot infer the number of online processors on
     unsupported or exotic systems. This should be a safer mode of operation.
     Proposed by Simon McVittie <smcv at debian.org>.
+  * Only preallocate disk size in dpkg for unpacked files bigger than 16 KiB.
+    Closes: #824636
   * Perl modules:
     - Validate architecture arguments in Dpkg::Deps deps_parse().
       Prompted by Johannes Schauer <josch at debian.org>.
diff --git a/lib/dpkg/fdio.c b/lib/dpkg/fdio.c
index 38781c8..b98596e 100644
--- a/lib/dpkg/fdio.c
+++ b/lib/dpkg/fdio.c
@@ -102,7 +102,9 @@ fd_allocate_size(int fd, off_t offset, off_t len)
 {
 	int rc;
 
-	if (len == 0)
+	/* Do not preallocate on very small files as that degrades performance
+	 * on some filesystems. */
+	if (len < (4 * 4096) - 1)
 		return 0;
 
 #if defined(HAVE_F_PREALLOCATE)

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