Re: [PATCH v4 6/6] elf: Don't cache symbol nor relocation tables with mmap

["H.J. Lu" <hjl.tools@gmail.com>]

On Thu, Mar 7, 2024 at 4:48 PM Sam James <sam@gentoo.org> wrote:
>
> "H.J. Lu" <hjl.tools@gmail.com> writes:
>
> > 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:
> >
> > FAIL: MIPS eh-frame 3
> >
> > in the linker testsuite for mipsisa32r2el-elf target, this is opt-in by
> > each backend.
> >
> >       * 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.
> >       (_bfd_elf_link_keep_memory): New.
> >       * libbfd-in.h (_bfd_link_keep_memory): Removed.
> >       * linker.c (_bfd_link_keep_memory): Likewise.
> >       * libbfd.h: Regenerated.
> > ---
> >  bfd/elf-bfd.h      |  3 ++
> >  bfd/elf32-i386.c   |  2 +-
> >  bfd/elf64-x86-64.c |  2 +-
> >  bfd/elflink.c      | 70 ++++++++++++++++++++++++++++++++++++++--------
> >  bfd/libbfd-in.h    |  3 --
> >  bfd/libbfd.h       |  3 --
> >  bfd/linker.c       | 35 -----------------------
> >  7 files changed, 63 insertions(+), 55 deletions(-)
> >
> > diff --git a/bfd/elf-bfd.h b/bfd/elf-bfd.h
> > index da7c5208017..6ed6f13cba2 100644
> > --- a/bfd/elf-bfd.h
> > +++ b/bfd/elf-bfd.h
> > @@ -3144,6 +3144,9 @@ extern bool _bfd_elf_mmap_section
> >  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 8aa1533d0ba..606e38b472c 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 f1e06040a5a..e52fa932ffc 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 4602fb3d10f..d7f5fe90017 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 +15597,51 @@ _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
> > +
> > +     FAIL: MIPS eh-frame 3
> > +
> > +     in the linker testsuite for mipsisa32r2el-elf target, this is
> > +     opt-in by each backend.  */
>
> Please add a reference to PR31458.

Will change it to

 /* 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;
> > +}
> > diff --git a/bfd/libbfd-in.h b/bfd/libbfd-in.h
> > index effe1b86b53..f89de00b551 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 c80f5a86ed1..3ed2e55a34b 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;
> > -}



-- 
H.J.