diff mbox series

[v12,4/6] elf: Don't cache symbol nor relocation tables with mmap

Message ID 20240317121912.799372-5-hjl.tools@gmail.com
State Committed
Headers
Series elf: Use mmap to map in section contents |

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Commit Message

H.J. Lu March 17, 2024, 12:19 p.m. UTC 
  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.

bfd/

	* elf32-i386.c (elf_i386_scan_relocs): Remove
	_bfd_link_keep_memory.
	* elf64-x86-64.c (elf_x86_64_scan_relocs): Likewise.
	* elflink.c (_bfd_elf_link_keep_memory): New.
	(_bfd_elf_link_iterate_on_relocs): Replace _bfd_link_keep_memory
	with _bfd_elf_link_keep_memory.
	(elf_link_add_object_symbols): Likewise.
	(init_reloc_cookie): Likewise.
	(init_reloc_cookie_rels): Likewise.
	* libbfd-in.h (_bfd_link_keep_memory): Removed.
	* linker.c (_bfd_link_keep_memory): Likewise.
	* libbfd.h: Regenerated.
---
 bfd/elf32-i386.c   |  2 +-
 bfd/elf64-x86-64.c |  2 +-
 bfd/elflink.c      | 69 ++++++++++++++++++++++++++++++++++++++--------
 bfd/libbfd-in.h    |  3 --
 bfd/libbfd.h       |  3 --
 bfd/linker.c       | 35 -----------------------
 6 files changed, 59 insertions(+), 55 deletions(-)
diff mbox series

Patch

diff --git a/bfd/elf32-i386.c b/bfd/elf32-i386.c
index 0f963c373be..8a6c0fa9060 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_munmap_section_contents (sec, contents);
       else
 	{
diff --git a/bfd/elf64-x86-64.c b/bfd/elf64-x86-64.c
index 2e3f86840e5..7756c5b1744 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_munmap_section_contents (sec, contents);
       else
 	{
diff --git a/bfd/elflink.c b/bfd/elflink.c
index 9162df60bfa..dcbe6e1a18c 100644
--- a/bfd/elflink.c
+++ b/bfd/elflink.c
@@ -49,6 +49,53 @@  struct elf_info_failed
 static bool _bfd_elf_fix_symbol_flags
   (struct elf_link_hash_entry *, struct elf_info_failed *);
 
+/* Return false if linker should avoid caching relocation information
+   and symbol tables of input files in memory.  */
+
+static 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.  */
+  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;
+}
+
 asection *
 _bfd_elf_section_for_symbol (struct elf_reloc_cookie *cookie,
 			     unsigned long r_symndx,
@@ -4182,10 +4229,9 @@  _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;
 
@@ -5551,10 +5597,9 @@  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;
 
@@ -13614,7 +13659,7 @@  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
@@ -13651,9 +13696,9 @@  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;
diff --git a/bfd/libbfd-in.h b/bfd/libbfd-in.h
index 889b221a950..7bfc58f12d8 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 876c1f223c7..36fe6c0ebd0 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;
-}