Messages in this thread | | | Subject | Re: [PATCHv2 2/3] i915: convert to new mount API | From | Matthew Auld <> | Date | Thu, 8 Aug 2019 18:03:02 +0100 |
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On 08/08/2019 17:23, Chris Wilson wrote: > Quoting Hugh Dickins (2019-08-08 16:54:16) >> On Thu, 8 Aug 2019, Al Viro wrote: >>> On Wed, Aug 07, 2019 at 08:30:02AM +0200, Christoph Hellwig wrote: >>>> On Tue, Aug 06, 2019 at 12:50:10AM -0700, Hugh Dickins wrote: >>>>> Though personally I'm averse to managing "f"objects through >>>>> "m"interfaces, which can get ridiculous (notably, MADV_HUGEPAGE works >>>>> on the virtual address of a mapping, but the huge-or-not alignment of >>>>> that mapping must have been decided previously). In Google we do use >>>>> fcntls F_HUGEPAGE and F_NOHUGEPAGE to override on a per-file basis - >>>>> one day I'll get to upstreaming those. >>>> >>>> Such an interface seems very useful, although the two fcntls seem a bit >>>> odd. >>>> >>>> But I think the point here is that the i915 has its own somewhat odd >>>> instance of tmpfs. If we could pass the equivalent of the huge=* >>>> options to shmem_file_setup all that garbage (including the >>>> shmem_file_setup_with_mnt function) could go away. >>> >>> ... or follow shmem_file_super() with whatever that fcntl maps to >>> internally. I would really love to get rid of that i915 kludge. >> >> As to the immediate problem of i915_gemfs using remount_fs on linux-next, >> IIUC, all that is necessary at the moment is the deletions patch below >> (but I'd prefer that to come from the i915 folks). Since gemfs has no >> need to change the huge option from its default to its default. >> >> As to the future of when they get back to wanting huge pages in gemfs, >> yes, that can probably best be arranged by using the internals of an >> fcntl F_HUGEPAGE on those objects that would benefit from it. >> >> Though my intention there was that the "huge=never" default ought >> to continue to refuse to give huge pages, even when asked by fcntl. >> So a little hackery may still be required, to allow the i915_gemfs >> internal mount to get huge pages when a user mount would not. >> >> As to whether shmem_file_setup_with_mnt() needs to live: I've given >> that no thought, but accept that shm_mnt is such a ragbag of different >> usages, that i915 is right to prefer their own separate gemfs mount. >> >> Hugh >> >> --- mmotm/drivers/gpu/drm/i915/gem/i915_gemfs.c 2019-07-21 19:40:16.573703780 -0700 >> +++ linux/drivers/gpu/drm/i915/gem/i915_gemfs.c 2019-08-08 07:19:23.967689058 -0700 >> @@ -24,28 +24,6 @@ int i915_gemfs_init(struct drm_i915_priv >> if (IS_ERR(gemfs)) >> return PTR_ERR(gemfs); >> >> - /* >> - * Enable huge-pages for objects that are at least HPAGE_PMD_SIZE, most >> - * likely 2M. Note that within_size may overallocate huge-pages, if say >> - * we allocate an object of size 2M + 4K, we may get 2M + 2M, but under >> - * memory pressure shmem should split any huge-pages which can be >> - * shrunk. >> - */ >> - >> - if (has_transparent_hugepage()) { >> - struct super_block *sb = gemfs->mnt_sb; >> - /* FIXME: Disabled until we get W/A for read BW issue. */ >> - char options[] = "huge=never"; >> - int flags = 0; >> - int err; >> - >> - err = sb->s_op->remount_fs(sb, &flags, options); >> - if (err) { >> - kern_unmount(gemfs); >> - return err; >> - } >> - } > > That's perfectly fine; we should probably leave a hint as to why gemfs > exists and include the suggestion of looking at per-file hugepage > controls. > > Matthew, how does this affect your current plans? If at all? Fine with me.
> -Chris >
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