[PATCH v6 4/5] elf: Don't cache symbol nor relocation tables with mmap
H.J. Lu
hjl.tools@gmail.com
Sat Mar 9 16:28:17 GMT 2024
During a "-j 8" LLVM 17 debug build on a machine with 32GB RAM and 16GB
swap, ld was killed by kernel because of out of memory:
[79437.949336] oom-kill:constraint=CONSTRAINT_NONE,nodemask=(null),cpuset=/,mems_allowed=0,global_oom,task_memcg=/user.slice/user-1000.slice/session-9.scope,task=ld,pid=797431,uid=1000
[79437.949349] Out of memory: Killed process 797431 (ld) total-vm:9219600kB, anon-rss:6558156kB, file-rss:1792kB, shmem-rss:0kB, UID:1000 pgtables:17552kB oom_score_adj:0
Don't cache symbol nor relocation tables if they are mapped in. Data to
link the 3.5GB clang executable in LLVM 17 debug build on Linux/x86-64
with 32GB RAM is:
stdio mmap improvement
user 86.73 87.02 -0.3%
system 9.55 9.21 3.6%
total 100.40 97.66 0.7%
maximum set(GB) 17.34 13.14 24%
page faults 4047667 3042877 25%
and data to link the 275M cc1plus executable in GCC 14 stage 1 build is:
user 5.41 5.44 -0.5%
system 0.80 0.76 5%
total 6.25 6.26 -0.2%
maximum set(MB) 1323 968 27%
page faults 323451 236371 27%
These improve the overall system performance for parallel build by
reducing memory usage and page faults.
Also rename _bfd_link_keep_memory to _bfd_elf_link_keep_memory. Since
the --no-keep-memory linker option causes:
https://sourceware.org/bugzilla/show_bug.cgi?id=31458
this is opt-in by each backend. Add the --keep-memory linker option to
always cache the symbol and relocation tables to mitigate --no-keep-memory
bugs like:
https://sourceware.org/bugzilla/show_bug.cgi?id=31466
bfd/
* elf-bfd.h (_bfd_elf_link_keep_memory): New.
* elf32-i386.c (elf_i386_scan_relocs): Replace
_bfd_link_keep_memory with _bfd_elf_link_keep_memory.
* elf64-x86-64.c (elf_x86_64_scan_relocs): Likewise.
* elflink.c (_bfd_elf_link_iterate_on_relocs): Likewise.
(elf_link_add_object_symbols): Likewise.
(init_reloc_cookie): Likewise.
(init_reloc_cookie_rels): Likewise.
(_bfd_elf_link_keep_memory): New.
* libbfd-in.h (_bfd_link_keep_memory): Removed.
* linker.c (_bfd_link_keep_memory): Likewise.
* libbfd.h: Regenerated.
include/
* bfdlink.h (bfd_link_info): Add keep_memory_is_set.
ld/
* NEWS: Mention --keep-memory.
* ld.texi: Document --keep-memory.
* ldlex.h (option_values): Add OPTION_KEEP_MEMORY.
* lexsup.c (ld_options): Add --keep-memory.
(parse_args): Handle OPTION_KEEP_MEMORY and set
link_info.keep_memory_is_set for OPTION_NO_KEEP_MEMORY.
---
bfd/elf-bfd.h | 3 ++
bfd/elf32-i386.c | 2 +-
bfd/elf64-x86-64.c | 2 +-
bfd/elflink.c | 72 ++++++++++++++++++++++++++++++++++++++--------
bfd/libbfd-in.h | 3 --
bfd/libbfd.h | 3 --
bfd/linker.c | 35 ----------------------
include/bfdlink.h | 3 ++
ld/NEWS | 2 ++
ld/ld.texi | 14 +++++----
ld/ldlex.h | 3 +-
ld/lexsup.c | 11 +++++--
12 files changed, 90 insertions(+), 63 deletions(-)
diff --git a/bfd/elf-bfd.h b/bfd/elf-bfd.h
index e7c2cd19bed..b9ec590cd4e 100644
--- a/bfd/elf-bfd.h
+++ b/bfd/elf-bfd.h
@@ -3144,6 +3144,9 @@ extern bool _bfd_elf_mmap_section_contents
extern void _bfd_elf_munmap_section_contents
(asection *, void *);
+extern bool _bfd_elf_link_keep_memory
+ (struct bfd_link_info *);
+
/* Large common section. */
extern asection _bfd_elf_large_com_section;
diff --git a/bfd/elf32-i386.c b/bfd/elf32-i386.c
index 0f963c373be..d1bd11094de 100644
--- a/bfd/elf32-i386.c
+++ b/bfd/elf32-i386.c
@@ -1932,7 +1932,7 @@ elf_i386_scan_relocs (bfd *abfd,
if (elf_section_data (sec)->this_hdr.contents != contents)
{
- if (!converted && !_bfd_link_keep_memory (info))
+ if (!converted && !_bfd_elf_link_keep_memory (info))
_bfd_elf_munmap_section_contents (sec, contents);
else
{
diff --git a/bfd/elf64-x86-64.c b/bfd/elf64-x86-64.c
index 2e3f86840e5..5e1fad069d1 100644
--- a/bfd/elf64-x86-64.c
+++ b/bfd/elf64-x86-64.c
@@ -2590,7 +2590,7 @@ elf_x86_64_scan_relocs (bfd *abfd, struct bfd_link_info *info,
if (elf_section_data (sec)->this_hdr.contents != contents)
{
- if (!converted && !_bfd_link_keep_memory (info))
+ if (!converted && !_bfd_elf_link_keep_memory (info))
_bfd_elf_munmap_section_contents (sec, contents);
else
{
diff --git a/bfd/elflink.c b/bfd/elflink.c
index 2a0586722e8..e5f2c75cb74 100644
--- a/bfd/elflink.c
+++ b/bfd/elflink.c
@@ -4205,10 +4205,9 @@ _bfd_elf_link_iterate_on_relocs
|| bfd_is_abs_section (o->output_section))
continue;
- internal_relocs = _bfd_elf_link_info_read_relocs (abfd, info,
- o, NULL,
- NULL,
- _bfd_link_keep_memory (info));
+ internal_relocs = _bfd_elf_link_info_read_relocs
+ (abfd, info, o, NULL, NULL,
+ _bfd_elf_link_keep_memory (info));
if (internal_relocs == NULL)
return false;
@@ -5574,10 +5573,9 @@ elf_link_add_object_symbols (bfd *abfd, struct bfd_link_info *info)
&& (s->flags & SEC_DEBUGGING) != 0))
continue;
- internal_relocs = _bfd_elf_link_info_read_relocs (abfd, info,
- s, NULL,
- NULL,
- _bfd_link_keep_memory (info));
+ internal_relocs = _bfd_elf_link_info_read_relocs
+ (abfd, info, s, NULL, NULL,
+ _bfd_elf_link_keep_memory (info));
if (internal_relocs == NULL)
goto error_free_vers;
@@ -13630,7 +13628,7 @@ init_reloc_cookie (struct elf_reloc_cookie *cookie,
info->callbacks->einfo (_("%P%X: can not read symbols: %E\n"));
return false;
}
- if (_bfd_link_keep_memory (info) )
+ if (_bfd_elf_link_keep_memory (info) )
{
symtab_hdr->contents = (bfd_byte *) cookie->locsyms;
info->cache_size += (cookie->locsymcount
@@ -13667,9 +13665,9 @@ init_reloc_cookie_rels (struct elf_reloc_cookie *cookie,
}
else
{
- cookie->rels = _bfd_elf_link_info_read_relocs (abfd, info, sec,
- NULL, NULL,
- _bfd_link_keep_memory (info));
+ cookie->rels = _bfd_elf_link_info_read_relocs
+ (abfd, info, sec, NULL, NULL,
+ _bfd_elf_link_keep_memory (info));
if (cookie->rels == NULL)
return false;
cookie->rel = cookie->rels;
@@ -15599,3 +15597,53 @@ _bfd_elf_add_dynamic_tags (bfd *output_bfd, struct bfd_link_info *info,
return true;
}
+
+/* Return false if linker should avoid caching relocation information
+ and symbol tables of input files in memory. */
+
+bool
+_bfd_elf_link_keep_memory (struct bfd_link_info *info)
+{
+#ifdef USE_MMAP
+ /* Don't cache symbol nor relocation tables if they are mapped in.
+ NB: Since the --no-keep-memory linker option causes:
+
+ https://sourceware.org/bugzilla/show_bug.cgi?id=31458
+
+ this is opt-in by each backend. */
+ if (!info->keep_memory_is_set)
+ {
+ const struct elf_backend_data *bed
+ = get_elf_backend_data (info->output_bfd);
+ if (bed->use_mmap)
+ return false;
+ }
+#endif
+ bfd *abfd;
+ bfd_size_type size;
+
+ if (!info->keep_memory)
+ return false;
+
+ if (info->max_cache_size == (bfd_size_type) -1)
+ return true;
+
+ abfd = info->input_bfds;
+ size = info->cache_size;
+ do
+ {
+ if (size >= info->max_cache_size)
+ {
+ /* Over the limit. Reduce the memory usage. */
+ info->keep_memory = false;
+ return false;
+ }
+ if (!abfd)
+ break;
+ size += abfd->alloc_size;
+ abfd = abfd->link.next;
+ }
+ while (1);
+
+ return true;
+}
diff --git a/bfd/libbfd-in.h b/bfd/libbfd-in.h
index 9d5396a0354..8ad9d36e396 100644
--- a/bfd/libbfd-in.h
+++ b/bfd/libbfd-in.h
@@ -848,9 +848,6 @@ extern bfd_byte * _bfd_write_unsigned_leb128
extern struct bfd_link_info *_bfd_get_link_info (bfd *)
ATTRIBUTE_HIDDEN;
-extern bool _bfd_link_keep_memory (struct bfd_link_info *)
- ATTRIBUTE_HIDDEN;
-
extern uintptr_t _bfd_pagesize ATTRIBUTE_HIDDEN;
extern uintptr_t _bfd_pagesize_m1 ATTRIBUTE_HIDDEN;
extern uintptr_t _bfd_minimum_mmap_size ATTRIBUTE_HIDDEN;
diff --git a/bfd/libbfd.h b/bfd/libbfd.h
index 4b605c4ce6c..17a6095ba00 100644
--- a/bfd/libbfd.h
+++ b/bfd/libbfd.h
@@ -854,9 +854,6 @@ extern bfd_byte * _bfd_write_unsigned_leb128
extern struct bfd_link_info *_bfd_get_link_info (bfd *)
ATTRIBUTE_HIDDEN;
-extern bool _bfd_link_keep_memory (struct bfd_link_info *)
- ATTRIBUTE_HIDDEN;
-
extern uintptr_t _bfd_pagesize ATTRIBUTE_HIDDEN;
extern uintptr_t _bfd_pagesize_m1 ATTRIBUTE_HIDDEN;
extern uintptr_t _bfd_minimum_mmap_size ATTRIBUTE_HIDDEN;
diff --git a/bfd/linker.c b/bfd/linker.c
index 36cca9624c2..eb42a78b622 100644
--- a/bfd/linker.c
+++ b/bfd/linker.c
@@ -3556,38 +3556,3 @@ _bfd_nolink_bfd_define_start_stop (struct bfd_link_info *info ATTRIBUTE_UNUSED,
{
return (struct bfd_link_hash_entry *) _bfd_ptr_bfd_null_error (sec->owner);
}
-
-/* Return false if linker should avoid caching relocation infomation
- and symbol tables of input files in memory. */
-
-bool
-_bfd_link_keep_memory (struct bfd_link_info * info)
-{
- bfd *abfd;
- bfd_size_type size;
-
- if (!info->keep_memory)
- return false;
-
- if (info->max_cache_size == (bfd_size_type) -1)
- return true;
-
- abfd = info->input_bfds;
- size = info->cache_size;
- do
- {
- if (size >= info->max_cache_size)
- {
- /* Over the limit. Reduce the memory usage. */
- info->keep_memory = false;
- return false;
- }
- if (!abfd)
- break;
- size += abfd->alloc_size;
- abfd = abfd->link.next;
- }
- while (1);
-
- return true;
-}
diff --git a/include/bfdlink.h b/include/bfdlink.h
index eac07d78364..9397032c6dd 100644
--- a/include/bfdlink.h
+++ b/include/bfdlink.h
@@ -580,6 +580,9 @@ struct bfd_link_info
/* TRUE if commonpagesize is set on command-line. */
unsigned int commonpagesize_is_set : 1;
+ /* TRUE if keep_memory is set on command-line. */
+ unsigned int keep_memory_is_set : 1;
+
/* Char that may appear as the first char of a symbol, but should be
skipped (like symbol_leading_char) when looking up symbols in
wrap_hash. Used by PowerPC Linux for 'dot' symbols. */
diff --git a/ld/NEWS b/ld/NEWS
index f70d2157339..8751b177329 100644
--- a/ld/NEWS
+++ b/ld/NEWS
@@ -1,5 +1,7 @@
-*- text -*-
+* Add --keep-memory to always cache the symbol and relocation tables.
+
* Add -plugin-save-temps to store plugin intermediate files permanently.
Changes in 2.42:
diff --git a/ld/ld.texi b/ld/ld.texi
index 6f234752278..792fdf1c2f3 100644
--- a/ld/ld.texi
+++ b/ld/ld.texi
@@ -2140,13 +2140,17 @@ If the map file already exists then it will be overwritten by this
operation.
@cindex memory usage
+@kindex --keep-memory
@kindex --no-keep-memory
-@item --no-keep-memory
+@item --keep-memory
@command{ld} normally optimizes for speed over memory usage by caching the
-symbol tables of input files in memory. This option tells @command{ld} to
-instead optimize for memory usage, by rereading the symbol tables as
-necessary. This may be required if @command{ld} runs out of memory space
-while linking a large executable.
+symbol and relocation tables of input files in memory if @samp{mmap} isn't
+used to map them in. The @option{--no-keep-memory} option tells @command{ld}
+to instead optimize for memory usage, by rereading the symbol and
+relocation tables as necessary. This may be required if @command{ld}
+runs out of memory space while linking a large executable.
+The @option{--keep-memory} option tells @command{ld} to always cache the
+symbol and relocation tables.
@kindex --no-undefined
@kindex -z defs
diff --git a/ld/ldlex.h b/ld/ldlex.h
index d575562a357..49ac8552e1f 100644
--- a/ld/ldlex.h
+++ b/ld/ldlex.h
@@ -43,9 +43,10 @@ enum option_values
OPTION_NO_EXPORT_DYNAMIC,
OPTION_HELP,
OPTION_IGNORE,
+ OPTION_KEEP_MEMORY,
+ OPTION_NO_KEEP_MEMORY,
OPTION_MAP,
OPTION_NO_DEMANGLE,
- OPTION_NO_KEEP_MEMORY,
OPTION_NO_WARN_MISMATCH,
OPTION_NO_WARN_SEARCH_MISMATCH,
OPTION_NOINHIBIT_EXEC,
diff --git a/ld/lexsup.c b/ld/lexsup.c
index dad3b6059ed..96d37ca3093 100644
--- a/ld/lexsup.c
+++ b/ld/lexsup.c
@@ -383,14 +383,16 @@ static const struct ld_option ld_options[] =
'\0', NULL, N_("Print option help"), TWO_DASHES },
{ {"init", required_argument, NULL, OPTION_INIT},
'\0', N_("SYMBOL"), N_("Call SYMBOL at load-time"), ONE_DASH },
+ { {"keep-memory", no_argument, NULL, OPTION_KEEP_MEMORY},
+ '\0', NULL, N_("Use more memory and less disk I/O"), TWO_DASHES },
+ { {"no-keep-memory", no_argument, NULL, OPTION_NO_KEEP_MEMORY},
+ '\0', NULL, N_("Use less memory and more disk I/O"), TWO_DASHES },
{ {"Map", required_argument, NULL, OPTION_MAP},
'\0', N_("FILE/DIR"), N_("Write a linker map to FILE or DIR/<outputname>.map"), ONE_DASH },
{ {"no-define-common", no_argument, NULL, OPTION_NO_DEFINE_COMMON},
'\0', NULL, N_("Do not define Common storage"), TWO_DASHES },
{ {"no-demangle", no_argument, NULL, OPTION_NO_DEMANGLE },
'\0', NULL, N_("Do not demangle symbol names"), TWO_DASHES },
- { {"no-keep-memory", no_argument, NULL, OPTION_NO_KEEP_MEMORY},
- '\0', NULL, N_("Use less memory and more disk I/O"), TWO_DASHES },
{ {"no-undefined", no_argument, NULL, OPTION_NO_UNDEFINED},
'\0', NULL, N_("Do not allow unresolved references in object files"),
TWO_DASHES },
@@ -1091,8 +1093,13 @@ parse_args (unsigned argc, char **argv)
case OPTION_NO_PRINT_GC_SECTIONS:
link_info.print_gc_sections = false;
break;
+ case OPTION_KEEP_MEMORY:
+ link_info.keep_memory = true;
+ link_info.keep_memory_is_set = true;
+ break;
case OPTION_NO_KEEP_MEMORY:
link_info.keep_memory = false;
+ link_info.keep_memory_is_set = true;
break;
case OPTION_NO_UNDEFINED:
link_info.unresolved_syms_in_objects = RM_DIAGNOSE;
--
2.44.0
More information about the Binutils
mailing list