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-rw-r--r--src/xz/hardware.c32
-rw-r--r--src/xz/xz.119
2 files changed, 50 insertions, 1 deletions
diff --git a/src/xz/hardware.c b/src/xz/hardware.c
index ff32f6d30148..e746cf91a76f 100644
--- a/src/xz/hardware.c
+++ b/src/xz/hardware.c
@@ -68,9 +68,39 @@ hardware_memlimit_set(uint64_t new_memlimit,
new_memlimit = (uint32_t)new_memlimit * total_ram / 100;
}
- if (set_compress)
+ if (set_compress) {
memlimit_compress = new_memlimit;
+#if SIZE_MAX == UINT32_MAX
+ // FIXME?
+ //
+ // When running a 32-bit xz on a system with a lot of RAM and
+ // using a percentage-based memory limit, the result can be
+ // bigger than the 32-bit address space. Limiting the limit
+ // below SIZE_MAX for compression (not decompression) makes
+ // xz lower the compression settings (or number of threads)
+ // to a level that *might* work. In practice it has worked
+ // when using a 64-bit kernel that gives full 4 GiB address
+ // space to 32-bit programs. In other situations this might
+ // still be too high, like 32-bit kernels that may give much
+ // less than 4 GiB to a single application.
+ //
+ // So this is an ugly hack but I will keep it here while
+ // it does more good than bad.
+ //
+ // Use a value less than SIZE_MAX so that there's some room
+ // for the xz program and so on. Don't use 4000 MiB because
+ // it could look like someone mixed up base-2 and base-10.
+ const uint64_t limit_max = UINT64_C(4020) << 20;
+
+ // UINT64_MAX is a special case for the string "max" so
+ // that has to be handled specially.
+ if (memlimit_compress != UINT64_MAX
+ && memlimit_compress > limit_max)
+ memlimit_compress = limit_max;
+#endif
+ }
+
if (set_decompress)
memlimit_decompress = new_memlimit;
diff --git a/src/xz/xz.1 b/src/xz/xz.1
index 9dffdc6f82be..a4aaa0027ecb 100644
--- a/src/xz/xz.1
+++ b/src/xz/xz.1
@@ -1005,6 +1005,25 @@ instead of
until the details have been decided.
.RE
.IP ""
+For 32-bit
+.BR xz
+there is a special case: if the
+.I limit
+would be over
+.BR "4020\ MiB" ,
+the
+.I limit
+is set to
+.BR "4020\ MiB" .
+(The values
+.B 0
+and
+.B max
+aren't affected by this.
+A similar feature doesn't exist for decompression.)
+This can be helpful when a 32-bit executable has access
+to 4\ GiB address space while hopefully doing no harm in other situations.
+.IP ""
See also the section
.BR "Memory usage" .
.TP