Messages in this thread | | | Date | Wed, 30 Jun 2010 16:07:01 -0700 | Subject | Re: [Intel-gfx] [PATCH] drm/i915: Selectively enable self-reclaim | From | Linus Torvalds <> |
| |
On Wed, Jun 30, 2010 at 12:05 AM, Chris Wilson <chris@chris-wilson.co.uk> wrote: > > Reviewing the patch again, we no longer set the default gfpmask on the > inode to contain NORETRY and instead add the NORETRY at the one spot in > the code where we are trying to do a large allocation and our shrinker > would be prevented from running (due to contention on struct_mutex). > > I do not know how this causes memory corruption across hibernate and would > appreciate any insights.
Hmm. More likely is the __GFP_MOVABLE flag, I think.
That commit changes the page cache allocation to use
+ mapping_gfp_mask (mapping) | + __GFP_COLD | + gfpmask);
if I read it right. And the default mapping_gfp_mask() is GFP_HIGHUSER_MOVABLE, so I think you get all of (__GFP_WAIT | __GFP_IO | __GFP_FS | __GFP_HARDWALL | __GFP_HIGHMEM) set by default.
The old code didn't just play games with ~__GFP_NORETRY and change that at runtime (which was buggy - no locking, no protection, no nothing), it also initialized the gfp mask. And that code also got removed:
- /* Basically we want to disable the OOM killer and handle ENOMEM - * ourselves by sacrificing pages from cached buffers. - * XXX shmem_file_[gs]et_gfp_mask() - */ - mapping_set_gfp_mask(obj->filp->f_path.dentry->d_inode->i_mapping, - GFP_HIGHUSER | - __GFP_COLD | - __GFP_FS | - __GFP_RECLAIMABLE | - __GFP_NORETRY | - __GFP_NOWARN | - __GFP_NOMEMALLOC);
(and note how it doesn't have __GFP_MOVABLE set).
So I wonder if we shouldn't re-instate that mapping_set_gfp_mask() for the _initial_ setting when the file descriptor is created. That part wasn't the bug - the bug was the code that used to try to do that whole per-allocation dance with the bits incorrectly (ie this part of the change:
- gfp = i915_gem_object_get_page_gfp_mask(obj); - i915_gem_object_set_page_gfp_mask(obj, gfp & ~__GFP_NORETRY); - ret = i915_gem_object_get_pages(obj); - i915_gem_object_set_page_gfp_mask (obj, gfp);
in that patch).
I could easily see that something would get very unhappy and corrupt memory if the suspend-to-disk phase ends up compacting memory and moving the pages around from under the i915 driver.
I dunno. But that seems more likely than the __GFP_NORETRY flag, which should have no semantic meaning (except making it more likely for allocations to fail, of course, but that's what the i915 code _wanted_).
Linus
| |