From: Tvrtko Ursulin tvrtko.ursulin@intel.com
This effectively removes writeback which was added in 2d6692e642e7 ("drm/i915: Start writeback from the shrinker").
Digging through the history it seems we went back and forth on the topic of whether it would be safe a couple of times. See for instance 5537252b6b6d ("drm/i915: Invalidate our pages under memory pressure") where Hugh Dickins has advised against it. I do not have enough expertise in the memory management area so am hoping for expert input here.
Reason for proposing removal is that there are reports from the field which indicate a sysetm wide deadlock (of a sort) implicating i915 doing writeback at shrinking time.
Signature is a hung task notifier kicking in and task traces such as:
[ 247.030274] minijail-init D 0 1773 1770 0x80004082 [ 247.036419] Call Trace: [ 247.039167] __schedule+0x57e/0x10d2 [ 247.043175] ? __schedule+0x586/0x10d2 [ 247.047381] ? _raw_spin_unlock+0xe/0x20 [ 247.051779] ? __queue_work+0x316/0x371 [ 247.056079] schedule+0x7c/0x9f [ 247.059602] rwsem_down_write_slowpath+0x2ae/0x494 [ 247.064971] unregister_shrinker+0x20/0x65 [ 247.069562] deactivate_locked_super+0x38/0x88 [ 247.074538] cleanup_mnt+0xcc/0x10e [ 247.078447] task_work_run+0x7d/0xa6 [ 247.082459] do_exit+0x23d/0x831 [ 247.086079] ? syscall_trace_enter+0x207/0x20e [ 247.091055] do_group_exit+0x8d/0x9d [ 247.095062] __x64_sys_exit_group+0x17/0x17 [ 247.099750] do_syscall_64+0x54/0x7e [ 247.103758] entry_SYSCALL_64_after_hwframe+0x44/0xa9
[ 246.876816] chrome D 0 1791 1785 0x00004080 [ 246.882965] Call Trace: [ 246.885713] __schedule+0x57e/0x10d2 [ 246.889724] ? pcpu_alloc_area+0x25d/0x273 [ 246.894314] schedule+0x7c/0x9f [ 246.897836] rwsem_down_write_slowpath+0x2ae/0x494 [ 246.903207] register_shrinker_prepared+0x19/0x48 [ 246.908479] ? test_single_super+0x10/0x10 [ 246.913071] sget_fc+0x1fc/0x20e [ 246.916691] ? kill_litter_super+0x40/0x40 [ 246.921334] ? proc_apply_options+0x42/0x42 [ 246.926044] vfs_get_super+0x3a/0xdf [ 246.930053] vfs_get_tree+0x2b/0xc3 [ 246.933965] fc_mount+0x12/0x39 [ 246.937492] pid_ns_prepare_proc+0x9d/0xc5 [ 246.942085] alloc_pid+0x275/0x289 [ 246.945900] copy_process+0x5e5/0xeea [ 246.950006] _do_fork+0x95/0x303 [ 246.953628] __se_sys_clone+0x65/0x7f [ 246.957735] do_syscall_64+0x54/0x7e [ 246.961743] entry_SYSCALL_64_after_hwframe+0x44/0xa9
And finally the smoking gun in:
[ 247.383338] CPU: 3 PID: 88 Comm: kswapd0 Tainted: G U 5.4.154 #36 [ 247.383338] Hardware name: Google Delbin/Delbin, BIOS Google_Delbin.13672.57.0 02/09/2021 [ 247.383339] RIP: 0010:__rcu_read_lock+0x0/0x1a [ 247.383339] Code: ff ff 0f 0b e9 61 fe ff ff 0f 0b e9 76 fe ff ff 0f 0b 49 8b 44 24 20 e9 59 ff ff ff 0f 0b e9 67 ff ff ff 0f 0b e9 1b ff ff ff <0f> 1f 44 00 00 55 48 89 e5 65 48 8b 04 25 80 5d 01 00 ff 80 f8 03 [ 247.383340] RSP: 0018:ffffb0aa0031b978 EFLAGS: 00000286 [ 247.383340] RAX: 0000000000000000 RBX: fffff6b944ca8040 RCX: fffff6b944ca8001 [ 247.383341] RDX: 0000000000000028 RSI: 0000000000000001 RDI: ffff8b52bc618c18 [ 247.383341] RBP: ffffb0aa0031b9d0 R08: 0000000000000000 R09: ffff8b52fb5f00d8 [ 247.383341] R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000 [ 247.383342] R13: 61c8864680b583eb R14: 0000000000000001 R15: ffffb0aa0031b980 [ 247.383342] FS: 0000000000000000(0000) GS:ffff8b52fbf80000(0000) knlGS:0000000000000000 [ 247.383343] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 247.383343] CR2: 00007c78a400d680 CR3: 0000000120f46006 CR4: 0000000000762ee0 [ 247.383344] PKRU: 55555554 [ 247.383344] Call Trace: [ 247.383345] find_get_entry+0x4c/0x116 [ 247.383345] find_lock_entry+0xc8/0xec [ 247.383346] shmem_writeback+0x7b/0x163 [ 247.383346] i915_gem_shrink+0x302/0x40b [ 247.383347] ? __intel_runtime_pm_get+0x22/0x82 [ 247.383347] i915_gem_shrinker_scan+0x86/0xa8 [ 247.383348] shrink_slab+0x272/0x48b [ 247.383348] shrink_node+0x784/0xbea [ 247.383348] ? rcu_read_unlock_special+0x66/0x15f [ 247.383349] ? update_batch_size+0x78/0x78 [ 247.383349] kswapd+0x75c/0xa56 [ 247.383350] kthread+0x147/0x156 [ 247.383350] ? kswapd_run+0xb6/0xb6 [ 247.383351] ? kthread_blkcg+0x2e/0x2e [ 247.383351] ret_from_fork+0x1f/0x40
You will notice the trace is from an older kernel, the problem being reproducing the issue on latest upstream base is proving to be tricky due other (unrelated) issues.
It is even tricky to repro on an older kernel, with it seemingly needing a very specific game, transparent huge pages enabled and a specific memory configuration.
However given the history on the topic I could find, assuming what I found is not incomplete, suspicion on writeback being not the right thing to do in general is still there. I would therefore like to have input from the experts here.
Signed-off-by: Tvrtko Ursulin tvrtko.ursulin@intel.com Fixes: 2d6692e642e7 ("drm/i915: Start writeback from the shrinker") References: 5537252b6b6d ("drm/i915: Invalidate our pages under memory pressure") Cc: Chris Wilson chris@chris-wilson.co.uk Cc: Mika Kuoppala mika.kuoppala@linux.intel.com Cc: Joonas Lahtinen joonas.lahtinen@linux.intel.com Cc: Tvrtko Ursulin tvrtko.ursulin@intel.com Cc: Matthew Auld matthew.auld@intel.com Cc: Daniel Vetter daniel.vetter@ffwll.ch Cc: Michal Hocko mhocko@suse.com Cc: Joonas Lahtinen joonas.lahtinen@linux.intel.com #v1 Cc: Jani Nikula jani.nikula@linux.intel.com Cc: Rodrigo Vivi rodrigo.vivi@intel.com Cc: Tvrtko Ursulin tvrtko.ursulin@linux.intel.com Cc: Thomas Hellström thomas.hellstrom@linux.intel.com Cc: Hugh Dickins hughd@google.com Cc: Sushma Venkatesh Reddy sushma.venkatesh.reddy@intel.com Cc: Renato Pereyra renatopereyra@google.com Cc: intel-gfx@lists.freedesktop.org Cc: stable@vger.kernel.org # v5.3+ --- drivers/gpu/drm/i915/gem/i915_gem_object.h | 2 - .../gpu/drm/i915/gem/i915_gem_object_types.h | 4 +- drivers/gpu/drm/i915/gem/i915_gem_pages.c | 10 ---- drivers/gpu/drm/i915/gem/i915_gem_shmem.c | 49 ------------------- drivers/gpu/drm/i915/gem/i915_gem_shrinker.c | 18 +++---- drivers/gpu/drm/i915/gem/i915_gem_shrinker.h | 1 - drivers/gpu/drm/i915/gem/i915_gem_ttm.c | 6 +-- .../gpu/drm/i915/gem/selftests/huge_pages.c | 3 +- 8 files changed, 11 insertions(+), 82 deletions(-)
diff --git a/drivers/gpu/drm/i915/gem/i915_gem_object.h b/drivers/gpu/drm/i915/gem/i915_gem_object.h index 66f20b803b01..352c7158a487 100644 --- a/drivers/gpu/drm/i915/gem/i915_gem_object.h +++ b/drivers/gpu/drm/i915/gem/i915_gem_object.h @@ -455,7 +455,6 @@ i915_gem_object_unpin_pages(struct drm_i915_gem_object *obj)
int __i915_gem_object_put_pages(struct drm_i915_gem_object *obj); int i915_gem_object_truncate(struct drm_i915_gem_object *obj); -void i915_gem_object_writeback(struct drm_i915_gem_object *obj);
/** * i915_gem_object_pin_map - return a contiguous mapping of the entire object @@ -621,7 +620,6 @@ int shmem_sg_alloc_table(struct drm_i915_private *i915, struct sg_table *st, unsigned int max_segment); void shmem_sg_free_table(struct sg_table *st, struct address_space *mapping, bool dirty, bool backup); -void __shmem_writeback(size_t size, struct address_space *mapping);
#ifdef CONFIG_MMU_NOTIFIER static inline bool diff --git a/drivers/gpu/drm/i915/gem/i915_gem_object_types.h b/drivers/gpu/drm/i915/gem/i915_gem_object_types.h index f9f7e44099fe..e188d6137cc0 100644 --- a/drivers/gpu/drm/i915/gem/i915_gem_object_types.h +++ b/drivers/gpu/drm/i915/gem/i915_gem_object_types.h @@ -57,10 +57,8 @@ struct drm_i915_gem_object_ops { void (*put_pages)(struct drm_i915_gem_object *obj, struct sg_table *pages); int (*truncate)(struct drm_i915_gem_object *obj); - void (*writeback)(struct drm_i915_gem_object *obj); int (*shrinker_release_pages)(struct drm_i915_gem_object *obj, - bool no_gpu_wait, - bool should_writeback); + bool no_gpu_wait);
int (*pread)(struct drm_i915_gem_object *obj, const struct drm_i915_gem_pread *arg); diff --git a/drivers/gpu/drm/i915/gem/i915_gem_pages.c b/drivers/gpu/drm/i915/gem/i915_gem_pages.c index 49c6e55c68ce..52e975f57956 100644 --- a/drivers/gpu/drm/i915/gem/i915_gem_pages.c +++ b/drivers/gpu/drm/i915/gem/i915_gem_pages.c @@ -168,16 +168,6 @@ int i915_gem_object_truncate(struct drm_i915_gem_object *obj) return 0; }
-/* Try to discard unwanted pages */ -void i915_gem_object_writeback(struct drm_i915_gem_object *obj) -{ - assert_object_held_shared(obj); - GEM_BUG_ON(i915_gem_object_has_pages(obj)); - - if (obj->ops->writeback) - obj->ops->writeback(obj); -} - static void __i915_gem_object_reset_page_iter(struct drm_i915_gem_object *obj) { struct radix_tree_iter iter; diff --git a/drivers/gpu/drm/i915/gem/i915_gem_shmem.c b/drivers/gpu/drm/i915/gem/i915_gem_shmem.c index cc9fe258fba7..b4b8c921063e 100644 --- a/drivers/gpu/drm/i915/gem/i915_gem_shmem.c +++ b/drivers/gpu/drm/i915/gem/i915_gem_shmem.c @@ -283,54 +283,6 @@ shmem_truncate(struct drm_i915_gem_object *obj) return 0; }
-void __shmem_writeback(size_t size, struct address_space *mapping) -{ - struct writeback_control wbc = { - .sync_mode = WB_SYNC_NONE, - .nr_to_write = SWAP_CLUSTER_MAX, - .range_start = 0, - .range_end = LLONG_MAX, - .for_reclaim = 1, - }; - unsigned long i; - - /* - * Leave mmapings intact (GTT will have been revoked on unbinding, - * leaving only CPU mmapings around) and add those pages to the LRU - * instead of invoking writeback so they are aged and paged out - * as normal. - */ - - /* Begin writeback on each dirty page */ - for (i = 0; i < size >> PAGE_SHIFT; i++) { - struct page *page; - - page = find_lock_page(mapping, i); - if (!page) - continue; - - if (!page_mapped(page) && clear_page_dirty_for_io(page)) { - int ret; - - SetPageReclaim(page); - ret = mapping->a_ops->writepage(page, &wbc); - if (!PageWriteback(page)) - ClearPageReclaim(page); - if (!ret) - goto put; - } - unlock_page(page); -put: - put_page(page); - } -} - -static void -shmem_writeback(struct drm_i915_gem_object *obj) -{ - __shmem_writeback(obj->base.size, obj->base.filp->f_mapping); -} - void __i915_gem_object_release_shmem(struct drm_i915_gem_object *obj, struct sg_table *pages, @@ -503,7 +455,6 @@ const struct drm_i915_gem_object_ops i915_gem_shmem_ops = { .get_pages = shmem_get_pages, .put_pages = shmem_put_pages, .truncate = shmem_truncate, - .writeback = shmem_writeback,
.pwrite = shmem_pwrite, .pread = shmem_pread, diff --git a/drivers/gpu/drm/i915/gem/i915_gem_shrinker.c b/drivers/gpu/drm/i915/gem/i915_gem_shrinker.c index 157a9765f483..99a38e016780 100644 --- a/drivers/gpu/drm/i915/gem/i915_gem_shrinker.c +++ b/drivers/gpu/drm/i915/gem/i915_gem_shrinker.c @@ -55,12 +55,11 @@ static bool unsafe_drop_pages(struct drm_i915_gem_object *obj, return false; }
-static int try_to_writeback(struct drm_i915_gem_object *obj, unsigned int flags) +static int obj_invalidate(struct drm_i915_gem_object *obj, unsigned int flags) { if (obj->ops->shrinker_release_pages) return obj->ops->shrinker_release_pages(obj, - !(flags & I915_SHRINK_ACTIVE), - flags & I915_SHRINK_WRITEBACK); + !(flags & I915_SHRINK_ACTIVE));
switch (obj->mm.madv) { case I915_MADV_DONTNEED: @@ -70,8 +69,9 @@ static int try_to_writeback(struct drm_i915_gem_object *obj, unsigned int flags) return 0; }
- if (flags & I915_SHRINK_WRITEBACK) - i915_gem_object_writeback(obj); + if (obj->base.filp) + invalidate_mapping_pages(file_inode(obj->base.filp)->i_mapping, + 0, (loff_t)-1);
return 0; } @@ -227,7 +227,7 @@ i915_gem_shrink(struct i915_gem_ww_ctx *ww, }
if (!__i915_gem_object_put_pages(obj)) { - if (!try_to_writeback(obj, shrink)) + if (!obj_invalidate(obj, shrink)) count += obj->base.size >> PAGE_SHIFT; } if (!ww) @@ -339,8 +339,7 @@ i915_gem_shrinker_scan(struct shrinker *shrinker, struct shrink_control *sc) &sc->nr_scanned, I915_SHRINK_ACTIVE | I915_SHRINK_BOUND | - I915_SHRINK_UNBOUND | - I915_SHRINK_WRITEBACK); + I915_SHRINK_UNBOUND); } }
@@ -361,8 +360,7 @@ i915_gem_shrinker_oom(struct notifier_block *nb, unsigned long event, void *ptr) with_intel_runtime_pm(&i915->runtime_pm, wakeref) freed_pages += i915_gem_shrink(NULL, i915, -1UL, NULL, I915_SHRINK_BOUND | - I915_SHRINK_UNBOUND | - I915_SHRINK_WRITEBACK); + I915_SHRINK_UNBOUND);
/* Because we may be allocating inside our own driver, we cannot * assert that there are no objects with pinned pages that are not diff --git a/drivers/gpu/drm/i915/gem/i915_gem_shrinker.h b/drivers/gpu/drm/i915/gem/i915_gem_shrinker.h index 8512470f6fd6..789d6947f9b9 100644 --- a/drivers/gpu/drm/i915/gem/i915_gem_shrinker.h +++ b/drivers/gpu/drm/i915/gem/i915_gem_shrinker.h @@ -22,7 +22,6 @@ unsigned long i915_gem_shrink(struct i915_gem_ww_ctx *ww, #define I915_SHRINK_BOUND BIT(1) #define I915_SHRINK_ACTIVE BIT(2) #define I915_SHRINK_VMAPS BIT(3) -#define I915_SHRINK_WRITEBACK BIT(4)
unsigned long i915_gem_shrink_all(struct drm_i915_private *i915); void i915_gem_driver_register__shrinker(struct drm_i915_private *i915); diff --git a/drivers/gpu/drm/i915/gem/i915_gem_ttm.c b/drivers/gpu/drm/i915/gem/i915_gem_ttm.c index 218a9b3037c7..b7ca7b66afe7 100644 --- a/drivers/gpu/drm/i915/gem/i915_gem_ttm.c +++ b/drivers/gpu/drm/i915/gem/i915_gem_ttm.c @@ -425,8 +425,7 @@ int i915_ttm_purge(struct drm_i915_gem_object *obj) }
static int i915_ttm_shrinker_release_pages(struct drm_i915_gem_object *obj, - bool no_wait_gpu, - bool should_writeback) + bool no_wait_gpu) { struct ttm_buffer_object *bo = i915_gem_to_ttm(obj); struct i915_ttm_tt *i915_tt = @@ -467,9 +466,6 @@ static int i915_ttm_shrinker_release_pages(struct drm_i915_gem_object *obj, return ret; }
- if (should_writeback) - __shmem_writeback(obj->base.size, i915_tt->filp->f_mapping); - return 0; }
diff --git a/drivers/gpu/drm/i915/gem/selftests/huge_pages.c b/drivers/gpu/drm/i915/gem/selftests/huge_pages.c index c69c7d45aabc..24bbf4d6a63d 100644 --- a/drivers/gpu/drm/i915/gem/selftests/huge_pages.c +++ b/drivers/gpu/drm/i915/gem/selftests/huge_pages.c @@ -1647,8 +1647,7 @@ static int igt_shrink_thp(void *arg) i915_gem_shrink(NULL, i915, -1UL, NULL, I915_SHRINK_BOUND | I915_SHRINK_UNBOUND | - I915_SHRINK_ACTIVE | - I915_SHRINK_WRITEBACK); + I915_SHRINK_ACTIVE); if (should_swap == i915_gem_object_has_pages(obj)) { pr_err("unexpected pages mismatch, should_swap=%s\n", yesno(should_swap));