On Sat, Apr 15, 2023 at 11:41:28PM -0700, Luis Chamberlain wrote: > On Sat, Apr 15, 2023 at 11:04:12PM -0700, Christoph Hellwig wrote: > > On Thu, Apr 13, 2023 at 10:28:40PM -0700, Luis Chamberlain wrote: > > > With this we run into 0 wasted virtual memory bytes. > > > > Avoid what duplicates? > > David Hildenbrand had reported that with over 400 CPUs vmap space > runs out and it seems it was related to module loading. I took a > look and confirmed it. Module loading ends up requiring in the > worst case 3 vmalloc allocations, so typically at least twice > the size of the module size and in the worst case just add > the decompressed module size: > > a) initial kernel_read*() call > b) optional module decompression > c) the actual module data copy we will keep > > Duplicate module requests that come from userspace end up being thrown > in the trash bin, as only one module will be allocated. Although there > are checks for a module prior to requesting a module udev still doesn't > do the best of a job to avoid that and so we end up with tons of > duplicate module requests. We're talking about gigabytes of vmalloc > bytes just lost because of this for large systems and megabytes for > average systems. So for example with just 255 CPUs we can loose about > 13.58 GiB, and for 8 CPUs about 226.53 MiB. How does the memory get "lost"? Shouldn't it be properly freed when the duplicate module load fails? thanks, greg k-h
