On Tue, Jan 16, 2024 at 4:09 AM Jiri Slaby <jirislaby@xxxxxxxxxx> wrote: > > On 16. 01. 24, 12:53, Jiri Slaby wrote: > > Hi, > > > > On 09. 08. 22, 20:24, Rik van Riel wrote: > >> Align larger anonymous memory mappings on THP boundaries by > >> going through thp_get_unmapped_area if THPs are enabled for > >> the current process. > >> > >> With this patch, larger anonymous mappings are now THP aligned. > >> When a malloc library allocates a 2MB or larger arena, that > >> arena can now be mapped with THPs right from the start, which > >> can result in better TLB hit rates and execution time. > > > > This appears to break 32bit processes on x86_64 (at least). In > > particular, 32bit kernel or firefox builds in our build system. > > > > Reverting this on top of 6.7 makes it work again. > > > > Downstream report: > > https://bugzilla.suse.com/show_bug.cgi?id=1218841 > > > > So running: > > pahole -J --btf_gen_floats -j --lang_exclude=rust > > --skip_encoding_btf_inconsistent_proto --btf_gen_optimized .tmp_vmlinux.btf > > > > crashes or errors out with some random errors: > > [182671] STRUCT idr's field 'idr_next' offset=128 bit_size=0 type=181346 > > Error emitting field > > > > strace shows mmap() fails with ENOMEM right before the errors: > > 1223 mmap2(NULL, 5783552, PROT_READ|PROT_WRITE, > > MAP_PRIVATE|MAP_ANONYMOUS, -1, 0 <unfinished ...> > > ... > > 1223 <... mmap2 resumed>) = -1 ENOMEM (Cannot allocate > > memory) It should be due to the virtual address space size on 32-bit machine. > > > > Note the .tmp_vmlinux.btf above can be arbitrary, but likely large > > enough. For reference, one is available at: > > https://decibel.fi.muni.cz/~xslaby/n/btf > > > > Any ideas? > > This works around the problem, of course (but is a band-aid, not a fix): > > --- a/mm/mmap.c > +++ b/mm/mmap.c > @@ -1829,7 +1829,7 @@ get_unmapped_area(struct file *file, unsigned long > addr, unsigned long len, > */ > pgoff = 0; > get_area = shmem_get_unmapped_area; > - } else if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE)) { > + } else if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) && > !in_32bit_syscall()) { > /* Ensures that larger anonymous mappings are THP > aligned. */ > get_area = thp_get_unmapped_area; > } > > > thp_get_unmapped_area() does not take care of the legacy stuff... Thanks for the report. I think we can just make thp_get_unmapped_area() no-op on 32 bit. > > regards, > -- > js > suse labs >
