[PATCH v4 6/6] elf: Don't cache symbol nor relocation tables with mmap
H.J. Lu
hjl.tools@gmail.com
Fri Mar 8 15:31:54 GMT 2024
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.
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