Re: [RFC PATCH 04/16] drm/ttm, drm/vmwgfx: Update the TTM swapout interface

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Am 15.02.23 um 19:19 schrieb Thomas Hellström:
On Wed, 2023-02-15 at 18:39 +0100, Christian König wrote:
Am 15.02.23 um 17:13 schrieb Thomas Hellström:
Update the TTM swapout interfaces for better compatibility with a
shrinker.
- Replace number-of-pages int return with a long to better match
the
    kernel's shrinker interface.
- The gfp_flags parameter to ttm_xx_swapout() currently only takes
the
    GFP_KERNEL value and shouldn't really be needed since the
shrinker we
    hook up in upcoming patches sets a allocation context to match
reclaim.
- Introduce a shrink reason enumeration and a driver callback to
shrink
    buffer objects.
Is that really necessary? This is mid-layering once more.

If drivers want to implement driver specific shrinking they should
register their own shrinker callback.
Yes, a choice needs to be made here. If TTM registers the shrinker, the
driver needs to be called at least to unbind and to remove dma-
mappings.

If the driver registers the shrinker it can still (I think) use the
pool helpers, but needs TTM for LRU traversal and accounting.

I can have a look at the latter if yout think that will be a better
solution.

Yeah, that's what I had in mind as well. Something like the drivers registers the shrinker and TTM provides the function to give a candidate for eviction.

Christian.


/Thomas


Christian.


    The TTM_SHRINK_WATERMARK reason is going to still be handled
using the
    existing shmem copy, and will be used by pool types that don't
lend
    themselves well to shinking (dma_alloc pool) and when drivers
explicitly
    requests swapout.
    The TTM_SHRINK_SWAP and TTM_SHRINK_PURGE reasons originate from
a
    shrinker and is to be handled by a new driver callback,
bo_shrink().
    Helpers for the new driver callback are provided in upcoming
patches.

Cc: linux-graphics-maintainer@xxxxxxxxxx
Signed-off-by: Thomas Hellström <thomas.hellstrom@xxxxxxxxxxxxxxx>
---
   drivers/gpu/drm/ttm/ttm_bo.c        | 38 ++++++++++++++++----
   drivers/gpu/drm/ttm/ttm_device.c    | 55 +++++++++++++++++++++---
-----
   drivers/gpu/drm/ttm/ttm_tt.c        | 23 ++++++------
   drivers/gpu/drm/vmwgfx/vmwgfx_drv.c |  3 +-
   include/drm/ttm/ttm_bo.h            |  4 +--
   include/drm/ttm/ttm_device.h        | 36 +++++++++++++++++--
   include/drm/ttm/ttm_tt.h            | 17 +++++++--
   7 files changed, 136 insertions(+), 40 deletions(-)

diff --git a/drivers/gpu/drm/ttm/ttm_bo.c
b/drivers/gpu/drm/ttm/ttm_bo.c
index 882c2fa346f3..e5c0970564c0 100644
--- a/drivers/gpu/drm/ttm/ttm_bo.c
+++ b/drivers/gpu/drm/ttm/ttm_bo.c
@@ -1114,13 +1114,29 @@ int ttm_bo_wait_ctx(struct
ttm_buffer_object *bo, struct ttm_operation_ctx *ctx)
   }
   EXPORT_SYMBOL(ttm_bo_wait_ctx);
-int ttm_bo_swapout(struct ttm_buffer_object *bo, struct
ttm_operation_ctx *ctx,
-                  gfp_t gfp_flags)
+/**
+ * ttm_bo_swapout() - Swap out or purge a buffer object
+ * @bo: The buffer object.
+ * @ctx: The ttm operation context.
+ * @reason: The swapout reason.
+ *
+ * Try to swap out or purge the contents of a system memory backed
buffer
+ * object. The function needs to be called with the device's LRU
lock held.
+ *
+ * Return: -EBUSY if the bo lock could not be grabbed or the
object was
+ * otherwise busy. Otherwise the number of pages swapped out or
negative
+ * error code on error. Iff the function didn't return -EBUSY, the
+ * LRU lock was dropped, and LRU traversal needs to restart.
+ */
+long ttm_bo_swapout(struct ttm_buffer_object *bo, struct
ttm_operation_ctx *ctx,
+                   enum ttm_shrink_reason reason)
   {
         struct ttm_place place;
         bool locked;
         long ret;
+       lockdep_assert_held(&bo->bdev->lru_lock);
+
         /*
          * While the bo may already reside in SYSTEM placement, set
          * SYSTEM as new placement to cover also the move further
below.
@@ -1142,8 +1158,12 @@ int ttm_bo_swapout(struct ttm_buffer_object
*bo, struct ttm_operation_ctx *ctx,
         }
        if (bo->deleted) {
+               long num_pages = bo->ttm->num_pages;
+
                 ret = ttm_bo_cleanup_refs(bo, false, false,
locked);
                 ttm_bo_put(bo);
+               if (!ret)
+                       return num_pages;
                 return ret == -EBUSY ? -ENOSPC : ret;
         }
@@ -1184,13 +1204,17 @@ int ttm_bo_swapout(struct ttm_buffer_object
*bo, struct ttm_operation_ctx *ctx,
          * Swap out. Buffer will be swapped in again as soon as
          * anyone tries to access a ttm page.
          */
-       if (bo->bdev->funcs->swap_notify)
-               bo->bdev->funcs->swap_notify(bo);
+       if (bo->bdev->funcs->bo_shrink && reason !=
TTM_SHRINK_WATERMARK) {
+               ret = bo->bdev->funcs->bo_shrink(bo, ctx);
+       } else {
+               if (bo->bdev->funcs->swap_notify)
+                       bo->bdev->funcs->swap_notify(bo);
+               ret = ttm_tt_swapout(bo->bdev, bo->ttm);
+               if (!ret)
+                       ret = bo->ttm->num_pages;
+       }
-       if (ttm_tt_is_populated(bo->ttm))
-               ret = ttm_tt_swapout(bo->bdev, bo->ttm, gfp_flags);
   out:
-
         /*
          * Unreserve without putting on LRU to avoid swapping out
an
          * already swapped buffer.
diff --git a/drivers/gpu/drm/ttm/ttm_device.c
b/drivers/gpu/drm/ttm/ttm_device.c
index ae2f19dc9f81..7eadea07027f 100644
--- a/drivers/gpu/drm/ttm/ttm_device.c
+++ b/drivers/gpu/drm/ttm/ttm_device.c
@@ -116,19 +116,28 @@ static int ttm_global_init(void)
         return ret;
   }
-/*
- * A buffer object shrink method that tries to swap out the first
- * buffer object on the global::swap_lru list.
+/**
+ * ttm_global_swapout() - Select and swap out a system-memory-
backed bo.
+ * @ctx: The operation context.
+ * @reason: The reason for swapout.
+ *
+ * Select, based on round-robin a TTM device and traverse the LRUs
of
+ * that specific device until a suitable bo backed by system
memory is found
+ * and swapped-out or purged.
+ *
+ * Return: Positive value or zero indicating the size in pages of
the
+ * bo swapped out. Negative error code on error.
    */
-int ttm_global_swapout(struct ttm_operation_ctx *ctx, gfp_t
gfp_flags)
+long ttm_global_swapout(struct ttm_operation_ctx *ctx,
+                       enum ttm_shrink_reason reason)
   {
         struct ttm_global *glob = &ttm_glob;
         struct ttm_device *bdev;
-       int ret = 0;
+       long ret = 0;
        mutex_lock(&ttm_global_mutex);
         list_for_each_entry(bdev, &glob->device_list, device_list)
{
-               ret = ttm_device_swapout(bdev, ctx, gfp_flags);
+               ret = ttm_device_swapout(bdev, ctx, reason);
                 if (ret > 0) {
                         list_move_tail(&bdev->device_list, &glob-
device_list);
                         break;
@@ -139,14 +148,29 @@ int ttm_global_swapout(struct
ttm_operation_ctx *ctx, gfp_t gfp_flags)
   }
   EXPORT_SYMBOL(ttm_global_swapout);
-int ttm_device_swapout(struct ttm_device *bdev, struct
ttm_operation_ctx *ctx,
-                      gfp_t gfp_flags)
+/**
+ * ttm_device_swapout() - Select and swap out a system-memory-
backed bo.
+ * @bdev: The device whos bos are considered for swapout.
+ * @ctx: The operation context.
+ * @reason: The reason for swapout.
+ *
+ * Traverse the LRUs of a specific device until a suitable bo
backed by
+ * system memory is found and swapped-out or purged.
+ *
+ * Return: Positive value or zero indicating the size in pages of
the
+ * bo swapped out. Negative error code on error.
+ */
+long ttm_device_swapout(struct ttm_device *bdev, struct
ttm_operation_ctx *ctx,
+                       enum ttm_shrink_reason reason)
   {
         struct ttm_resource_cursor cursor;
         struct ttm_resource_manager *man;
         struct ttm_resource *res;
         unsigned i;
-       int ret;
+       long ret;
+
+       if (reason != TTM_SHRINK_WATERMARK && !bdev->funcs-
bo_shrink)
+               return 0;
        spin_lock(&bdev->lru_lock);
         for (i = TTM_PL_SYSTEM; i < TTM_NUM_MEM_TYPES; ++i) {
@@ -156,16 +180,19 @@ int ttm_device_swapout(struct ttm_device
*bdev, struct ttm_operation_ctx *ctx,
                ttm_resource_manager_for_each_res(man, &cursor,
res) {
                         struct ttm_buffer_object *bo = res->bo;
-                       uint32_t num_pages;
+                       struct ttm_tt *tt;
                        if (!bo || bo->resource != res)
                                 continue;
-                       num_pages = PFN_UP(bo->base.size);
-                       ret = ttm_bo_swapout(bo, ctx, gfp_flags);
+                       tt = bo->ttm;
+                       if (!tt || (reason == TTM_SHRINK_PURGE &&
+                                   !ttm_tt_purgeable(tt)))
+                               continue;
+                       ret = ttm_bo_swapout(bo, ctx, reason);
                         /* ttm_bo_swapout has dropped the lru_lock
*/
-                       if (!ret)
-                               return num_pages;
+                       if (ret >= 0)
+                               return ret;
                         if (ret != -EBUSY)
                                 return ret;
                 }
diff --git a/drivers/gpu/drm/ttm/ttm_tt.c
b/drivers/gpu/drm/ttm/ttm_tt.c
index ab725d9d14a6..a68c14de0161 100644
--- a/drivers/gpu/drm/ttm/ttm_tt.c
+++ b/drivers/gpu/drm/ttm/ttm_tt.c
@@ -239,22 +239,21 @@ int ttm_tt_swapin(struct ttm_tt *ttm)
  /**
    * ttm_tt_swapout - swap out tt object
- *
    * @bdev: TTM device structure.
    * @ttm: The struct ttm_tt.
- * @gfp_flags: Flags to use for memory allocation.
    *
- * Swapout a TT object to a shmem_file, return number of pages
swapped out or
- * negative error code.
+ * Swapout a TT object to a shmem_file.
+ *
+ * Return: number of pages swapped out or negative error code on
error.
    */
-int ttm_tt_swapout(struct ttm_device *bdev, struct ttm_tt *ttm,
-                  gfp_t gfp_flags)
+int ttm_tt_swapout(struct ttm_device *bdev, struct ttm_tt *ttm)
   {
         loff_t size = (loff_t)ttm->num_pages << PAGE_SHIFT;
         struct address_space *swap_space;
         struct file *swap_storage;
         struct page *from_page;
         struct page *to_page;
+       gfp_t gfp_flags;
         int i, ret;
        swap_storage = shmem_file_setup("ttm swap", size, 0);
@@ -264,7 +263,7 @@ int ttm_tt_swapout(struct ttm_device *bdev,
struct ttm_tt *ttm,
         }
        swap_space = swap_storage->f_mapping;
-       gfp_flags &= mapping_gfp_mask(swap_space);
+       gfp_flags = GFP_KERNEL & mapping_gfp_mask(swap_space);
        for (i = 0; i < ttm->num_pages; ++i) {
                 from_page = ttm->pages[i];
@@ -315,12 +314,14 @@ int ttm_tt_populate(struct ttm_device *bdev,
         while (atomic_long_read(&ttm_pages_allocated) >
ttm_pages_limit ||
                atomic_long_read(&ttm_dma32_pages_allocated) >
                ttm_dma32_pages_limit) {
+               long r = ttm_global_swapout(ctx,
TTM_SHRINK_WATERMARK);
-               ret = ttm_global_swapout(ctx, GFP_KERNEL);
-               if (ret == 0)
+               if (!r)
                         break;
-               if (ret < 0)
+               if (r < 0) {
+                       ret = r;
                         goto error;
+               }
         }
        if (bdev->funcs->ttm_tt_populate)
@@ -379,7 +380,7 @@ static int ttm_tt_debugfs_shrink_show(struct
seq_file *m, void *data)
   {
         struct ttm_operation_ctx ctx = { false, false };
-       seq_printf(m, "%d\n", ttm_global_swapout(&ctx,
GFP_KERNEL));
+       seq_printf(m, "%ld\n", ttm_global_swapout(&ctx,
TTM_SHRINK_SWAP));
         return 0;
   }
   DEFINE_SHOW_ATTRIBUTE(ttm_tt_debugfs_shrink);
diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_drv.c
b/drivers/gpu/drm/vmwgfx/vmwgfx_drv.c
index 2588615a2a38..292c5199d2cc 100644
--- a/drivers/gpu/drm/vmwgfx/vmwgfx_drv.c
+++ b/drivers/gpu/drm/vmwgfx/vmwgfx_drv.c
@@ -1514,7 +1514,8 @@ static int vmw_pm_freeze(struct device *kdev)
         vmw_execbuf_release_pinned_bo(dev_priv);
         vmw_resource_evict_all(dev_priv);
         vmw_release_device_early(dev_priv);
-       while (ttm_device_swapout(&dev_priv->bdev, &ctx,
GFP_KERNEL) > 0);
+       while (ttm_device_swapout(&dev_priv->bdev, &ctx,
TTM_SHRINK_WATERMARK) > 0)
+               ;
         vmw_fifo_resource_dec(dev_priv);
         if (atomic_read(&dev_priv->num_fifo_resources) != 0) {
                 DRM_ERROR("Can't hibernate while 3D resources are
active.\n");
diff --git a/include/drm/ttm/ttm_bo.h b/include/drm/ttm/ttm_bo.h
index 8b113c384236..6b45e0b639e0 100644
--- a/include/drm/ttm/ttm_bo.h
+++ b/include/drm/ttm/ttm_bo.h
@@ -375,8 +375,8 @@ void ttm_bo_kunmap(struct ttm_bo_kmap_obj
*map);
   int ttm_bo_vmap(struct ttm_buffer_object *bo, struct iosys_map
*map);
   void ttm_bo_vunmap(struct ttm_buffer_object *bo, struct iosys_map
*map);
   int ttm_bo_mmap_obj(struct vm_area_struct *vma, struct
ttm_buffer_object *bo);
-int ttm_bo_swapout(struct ttm_buffer_object *bo, struct
ttm_operation_ctx *ctx,
-                  gfp_t gfp_flags);
+long ttm_bo_swapout(struct ttm_buffer_object *bo, struct
ttm_operation_ctx *ctx,
+                   enum ttm_shrink_reason reason);
   void ttm_bo_pin(struct ttm_buffer_object *bo);
   void ttm_bo_unpin(struct ttm_buffer_object *bo);
   int ttm_mem_evict_first(struct ttm_device *bdev,
diff --git a/include/drm/ttm/ttm_device.h
b/include/drm/ttm/ttm_device.h
index 4f3e81eac6f3..6bd2abf712ab 100644
--- a/include/drm/ttm/ttm_device.h
+++ b/include/drm/ttm/ttm_device.h
@@ -35,6 +35,21 @@ struct ttm_placement;
   struct ttm_buffer_object;
   struct ttm_operation_ctx;
+/**
+ * enum ttm_shrink_reason - Reason for shrinking system memory
+ * @TTM_SHRINK_WATERMARK - A watermark limit was reached. Not from
reclaim.
+ * @TTM_SHRINK_PURGE - A request for shrinking only purged
objects.
+ * @TTM_SHRINK_SWAP - A request for shrinking any object.
+ *
+ * This enum is intended for the buffer object- and shrink method
selection
+ * algorithms. It's not intended to leak to or be used by TTM
drivers.
+ */
+enum ttm_shrink_reason {
+       TTM_SHRINK_WATERMARK,
+       TTM_SHRINK_PURGE,
+       TTM_SHRINK_SWAP,
+};
+
   /**
    * struct ttm_global - Buffer object driver global data.
    */
@@ -207,6 +222,19 @@ struct ttm_device_funcs {
          * adding fences that may force a delayed delete
          */
         void (*release_notify)(struct ttm_buffer_object *bo);
+
+       /**
+        * Shrink the bo's system pages, Either by swapping or by
purging.
+        * @bo: Bo the system pages of which are to be shrunken.
+        * @ctx: Operation ctx. In particular the driver callback
should
+        *       adhere to the no_wait_gpu and interruptible
fields.
+        *
+        * This is also notifying the driver that the bo is about
to be
+        * shrunken and the driver should take care to unbind any
GPU bindings
+        * and to note that the content is purged if @bo->ttm is
purgeable.
+        */
+       long (*bo_shrink)(struct ttm_buffer_object *bo,
+                         struct ttm_operation_ctx *ctx);
   };
  /**
@@ -268,9 +296,11 @@ struct ttm_device {
         struct workqueue_struct *wq;
   };
-int ttm_global_swapout(struct ttm_operation_ctx *ctx, gfp_t
gfp_flags);
-int ttm_device_swapout(struct ttm_device *bdev, struct
ttm_operation_ctx *ctx,
-                      gfp_t gfp_flags);
+long ttm_global_swapout(struct ttm_operation_ctx *ctx,
+                       enum ttm_shrink_reason reason);
+
+long ttm_device_swapout(struct ttm_device *bdev, struct
ttm_operation_ctx *ctx,
+                       enum ttm_shrink_reason reason);
  static inline struct ttm_resource_manager *
   ttm_manager_type(struct ttm_device *bdev, int mem_type)
diff --git a/include/drm/ttm/ttm_tt.h b/include/drm/ttm/ttm_tt.h
index cc54be1912e1..627168eba8f6 100644
--- a/include/drm/ttm/ttm_tt.h
+++ b/include/drm/ttm/ttm_tt.h
@@ -87,6 +87,7 @@ struct ttm_tt {
   #define TTM_TT_FLAG_ZERO_ALLOC                BIT(1)
   #define TTM_TT_FLAG_EXTERNAL          BIT(2)
   #define TTM_TT_FLAG_EXTERNAL_MAPPABLE BIT(3)
+#define TTM_TT_FLAG_DONTNEED           BIT(4)
  #define TTM_TT_FLAG_PRIV_POPULATED    BIT(31)
         uint32_t page_flags;
@@ -180,8 +181,8 @@ void ttm_tt_destroy(struct ttm_device *bdev,
struct ttm_tt *ttm);
    * Swap in a previously swap out ttm_tt.
    */
   int ttm_tt_swapin(struct ttm_tt *ttm);
-int ttm_tt_swapout(struct ttm_device *bdev, struct ttm_tt *ttm,
-                  gfp_t gfp_flags);
+
+int ttm_tt_swapout(struct ttm_device *bdev, struct ttm_tt *ttm);
  /**
    * ttm_tt_populate - allocate pages for a ttm
@@ -223,6 +224,18 @@ void ttm_tt_mgr_init(unsigned long num_pages,
unsigned long num_dma32_pages);
   struct ttm_kmap_iter *ttm_kmap_iter_tt_init(struct
ttm_kmap_iter_tt *iter_tt,
                                             struct ttm_tt *tt);
+/**
+ * ttm_tt_purgeable() - Whether a struct ttm_tt's contents is
purgeable
+ * @tt: The struct ttm_tt to consider.
+ *
+ * Return: Whether the contents is purgeable in the sence that the
owner
+ * doesn't mind losing it as long as it gets notified.
+ */
+static inline bool ttm_tt_purgeable(struct ttm_tt *tt)
+{
+       return tt->page_flags & TTM_TT_FLAG_DONTNEED;
+}
+
   #if IS_ENABLED(CONFIG_AGP)
   #include <linux/agp_backend.h>




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