On Mon, Oct 09, 2017 at 03:51:06AM +0800, Yang Shi wrote: > > > On 10/8/17 5:56 AM, Kirill A. Shutemov wrote: > > On Sat, Oct 07, 2017 at 04:22:10AM +0800, Yang Shi wrote: > > > When passing "huge=always" option for mounting tmpfs, THP is supposed to > > > be allocated all the time when it can fit, but when the available space is > > > smaller than the size of THP (2MB on x86), shmem fault handler still tries > > > to allocate huge page every time, then fallback to regular 4K page > > > allocation, i.e.: > > > > > > # mount -t tmpfs -o huge,size=3000k tmpfs /tmp > > > # dd if=/dev/zero of=/tmp/test bs=1k count=2048 > > > # dd if=/dev/zero of=/tmp/test1 bs=1k count=2048 > > > > > > The last dd command will handle 952 times page fault handler, then exit > > > with -ENOSPC. > > > > > > Rounding up tmpfs size to THP size in order to use THP with "always" > > > more efficiently. And, it will not wast too much memory (just allocate > > > 511 extra pages in worst case). > > > > Hm. I don't think it's good idea to silently increase size of fs. > > How about printing a warning to say the filesystem is resized? > > > > > Maybe better just refuse to mount with huge=always for too small fs? > > It sounds fine too. When mounting tmpfs with "huge=always", if the size is > not THP size aligned, it just can refuse to mount, then show warning about > alignment restriction. Honestly, I wouldn't bother. Using filesystem at near-full capacity is not best practice. Performance penalty for doing is fair enough. And forcing alignment doesn't really fixes anything: user still allowed to fill the filesystem with files less than 2M in size. -- Kirill A. Shutemov -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
