| Message ID | 87fsi4hb2m.fsf@oldenburg.str.redhat.com |
|---|---|
| State | New |
| Headers | show |
| Series | malloc: Do not use MAP_NORESERVE to allocate heap segments | expand |
On 2022-08-10 02:22, Florian Weimer via Libc-alpha wrote: > Address space for heap segments is reserved in a mmap call with > MAP_ANONYMOUS | MAP_PRIVATE and protection flags PROT_NONE. This > reservation does not count against the RSS limit of the process or > system. Backing memory is allocated using mprotect in alloc_new_heap > and grow_heap, and at this point, the allocator expects the kernel > to provide memory (subject to memory overcommit). > > The SIGSEGV that might generate due to MAP_NORESERVE (according to > the mmap manual page) does not seem to occur in practice, it's always > SIGKILL from the OOM killer. Even if there is a way that SIGSEGV > could be generated, it is confusing to applications that this only > happens for secondary heaps, not for large mmap-based allocations, > and not for the main arena. > > --- > malloc/arena.c | 5 +---- > malloc/malloc.c | 4 ---- > 2 files changed, 1 insertion(+), 8 deletions(-) LGTM. Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org> > > diff --git a/malloc/arena.c b/malloc/arena.c > index defd25c8a6..074ecbc09f 100644 > --- a/malloc/arena.c > +++ b/malloc/arena.c > @@ -559,16 +559,13 @@ new_heap (size_t size, size_t top_pad) > #if HAVE_TUNABLES > if (__glibc_unlikely (mp_.hp_pagesize != 0)) > { > - /* MAP_NORESERVE is not used for huge pages because some kernel may > - not reserve the mmap region and a subsequent access may trigger > - a SIGBUS if there is no free pages in the pool. */ > heap_info *h = alloc_new_heap (size, top_pad, mp_.hp_pagesize, > mp_.hp_flags); > if (h != NULL) > return h; > } > #endif > - return alloc_new_heap (size, top_pad, GLRO (dl_pagesize), MAP_NORESERVE); > + return alloc_new_heap (size, top_pad, GLRO (dl_pagesize), 0); > } > > /* Grow a heap. size is automatically rounded up to a > diff --git a/malloc/malloc.c b/malloc/malloc.c > index 914052eb69..29fa71b3b2 100644 > --- a/malloc/malloc.c > +++ b/malloc/malloc.c > @@ -1110,10 +1110,6 @@ static mchunkptr mremap_chunk(mchunkptr p, size_t new_size); > # define MAP_ANONYMOUS MAP_ANON > #endif > > -#ifndef MAP_NORESERVE > -# define MAP_NORESERVE 0 > -#endif > - > #define MMAP(addr, size, prot, flags) \ > __mmap((addr), (size), (prot), (flags)|MAP_ANONYMOUS|MAP_PRIVATE, -1, 0) > >
diff --git a/malloc/arena.c b/malloc/arena.c index defd25c8a6..074ecbc09f 100644 --- a/malloc/arena.c +++ b/malloc/arena.c @@ -559,16 +559,13 @@ new_heap (size_t size, size_t top_pad) #if HAVE_TUNABLES if (__glibc_unlikely (mp_.hp_pagesize != 0)) { - /* MAP_NORESERVE is not used for huge pages because some kernel may - not reserve the mmap region and a subsequent access may trigger - a SIGBUS if there is no free pages in the pool. */ heap_info *h = alloc_new_heap (size, top_pad, mp_.hp_pagesize, mp_.hp_flags); if (h != NULL) return h; } #endif - return alloc_new_heap (size, top_pad, GLRO (dl_pagesize), MAP_NORESERVE); + return alloc_new_heap (size, top_pad, GLRO (dl_pagesize), 0); } /* Grow a heap. size is automatically rounded up to a diff --git a/malloc/malloc.c b/malloc/malloc.c index 914052eb69..29fa71b3b2 100644 --- a/malloc/malloc.c +++ b/malloc/malloc.c @@ -1110,10 +1110,6 @@ static mchunkptr mremap_chunk(mchunkptr p, size_t new_size); # define MAP_ANONYMOUS MAP_ANON #endif -#ifndef MAP_NORESERVE -# define MAP_NORESERVE 0 -#endif - #define MMAP(addr, size, prot, flags) \ __mmap((addr), (size), (prot), (flags)|MAP_ANONYMOUS|MAP_PRIVATE, -1, 0)