[PATCH v18 26/26] drm/panfrost: Switch to generic memory shrinker
Boris Brezillon
boris.brezillon at collabora.com
Fri Nov 24 10:04:40 UTC 2023
On Mon, 30 Oct 2023 02:02:05 +0300
Dmitry Osipenko <dmitry.osipenko at collabora.com> wrote:
> Replace Panfrost's custom memory shrinker with a common drm-shmem
> memory shrinker.
>
> Signed-off-by: Dmitry Osipenko <dmitry.osipenko at collabora.com>
> ---
> drivers/gpu/drm/panfrost/Makefile | 1 -
> drivers/gpu/drm/panfrost/panfrost_device.h | 4 -
> drivers/gpu/drm/panfrost/panfrost_drv.c | 27 ++--
> drivers/gpu/drm/panfrost/panfrost_gem.c | 34 +++--
> drivers/gpu/drm/panfrost/panfrost_gem.h | 9 --
> .../gpu/drm/panfrost/panfrost_gem_shrinker.c | 129 ------------------
> drivers/gpu/drm/panfrost/panfrost_job.c | 18 ++-
> drivers/gpu/drm/panfrost/panfrost_mmu.c | 18 ++-
> include/drm/drm_gem_shmem_helper.h | 7 -
Nice diffstat.
> 9 files changed, 66 insertions(+), 181 deletions(-)
> delete mode 100644 drivers/gpu/drm/panfrost/panfrost_gem_shrinker.c
>
> diff --git a/drivers/gpu/drm/panfrost/Makefile b/drivers/gpu/drm/panfrost/Makefile
> index 2c01c1e7523e..f2cb1ab0a32d 100644
> --- a/drivers/gpu/drm/panfrost/Makefile
> +++ b/drivers/gpu/drm/panfrost/Makefile
> @@ -5,7 +5,6 @@ panfrost-y := \
> panfrost_device.o \
> panfrost_devfreq.o \
> panfrost_gem.o \
> - panfrost_gem_shrinker.o \
> panfrost_gpu.o \
> panfrost_job.o \
> panfrost_mmu.o \
> diff --git a/drivers/gpu/drm/panfrost/panfrost_device.h b/drivers/gpu/drm/panfrost/panfrost_device.h
> index 1e85656dc2f7..2b24a0d4f85e 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_device.h
> +++ b/drivers/gpu/drm/panfrost/panfrost_device.h
> @@ -117,10 +117,6 @@ struct panfrost_device {
> atomic_t pending;
> } reset;
>
> - struct mutex shrinker_lock;
> - struct list_head shrinker_list;
> - struct shrinker shrinker;
> -
> struct panfrost_devfreq pfdevfreq;
>
> struct {
> diff --git a/drivers/gpu/drm/panfrost/panfrost_drv.c b/drivers/gpu/drm/panfrost/panfrost_drv.c
> index 7f2aba96d5b9..ef520d2cc1d2 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_drv.c
> +++ b/drivers/gpu/drm/panfrost/panfrost_drv.c
> @@ -171,7 +171,6 @@ panfrost_lookup_bos(struct drm_device *dev,
> break;
> }
>
> - atomic_inc(&bo->gpu_usecount);
> job->mappings[i] = mapping;
> }
>
> @@ -397,7 +396,6 @@ static int panfrost_ioctl_madvise(struct drm_device *dev, void *data,
> {
> struct panfrost_file_priv *priv = file_priv->driver_priv;
> struct drm_panfrost_madvise *args = data;
> - struct panfrost_device *pfdev = dev->dev_private;
> struct drm_gem_object *gem_obj;
> struct panfrost_gem_object *bo;
> int ret = 0;
> @@ -410,11 +408,15 @@ static int panfrost_ioctl_madvise(struct drm_device *dev, void *data,
>
> bo = to_panfrost_bo(gem_obj);
>
> + if (bo->is_heap) {
> + args->retained = 1;
> + goto out_put_object;
> + }
After digging a bit, I finally got why you do that:
panfrost_gem_shmem_is_purgeable() had a shmem->sgt != NULL test, and
shmem->sgt is never populated for heap BOs (those have a separate sgts
table, each entry containing an sgt covering a 2MB portion of the
buffer). Looking at the code, I don't think making heap BO
non-reclaimable was intentional, otherwise we'd have filtered it out in
panfrost_ioctl_madvise() to avoid inserting an element that will never
be reclaimable. TLDR; I understand why you do that, and I agree this is
the right thing to do (even if I doubt we have any userspace using the
MADV ioctl on heap BOs), but it definitely deserves a comment
explaining that this is here to keep a pre-existing behavior, so people
are not tempted to remove it, and if they do, they must have a good
explanation.
> +
> ret = dma_resv_lock_interruptible(bo->base.base.resv, NULL);
> if (ret)
> goto out_put_object;
>
> - mutex_lock(&pfdev->shrinker_lock);
> mutex_lock(&bo->mappings.lock);
> if (args->madv == PANFROST_MADV_DONTNEED) {
> struct panfrost_gem_mapping *first;
> @@ -440,17 +442,8 @@ static int panfrost_ioctl_madvise(struct drm_device *dev, void *data,
>
> args->retained = drm_gem_shmem_madvise_locked(&bo->base, args->madv);
>
> - if (args->retained) {
> - if (args->madv == PANFROST_MADV_DONTNEED)
> - list_move_tail(&bo->base.madv_list,
> - &pfdev->shrinker_list);
> - else if (args->madv == PANFROST_MADV_WILLNEED)
> - list_del_init(&bo->base.madv_list);
> - }
> -
> out_unlock_mappings:
> mutex_unlock(&bo->mappings.lock);
> - mutex_unlock(&pfdev->shrinker_lock);
> dma_resv_unlock(bo->base.base.resv);
> out_put_object:
> drm_gem_object_put(gem_obj);
> @@ -635,9 +628,6 @@ static int panfrost_probe(struct platform_device *pdev)
> ddev->dev_private = pfdev;
> pfdev->ddev = ddev;
>
> - mutex_init(&pfdev->shrinker_lock);
> - INIT_LIST_HEAD(&pfdev->shrinker_list);
> -
> err = panfrost_device_init(pfdev);
> if (err) {
> if (err != -EPROBE_DEFER)
> @@ -659,10 +649,14 @@ static int panfrost_probe(struct platform_device *pdev)
> if (err < 0)
> goto err_out1;
>
> - panfrost_gem_shrinker_init(ddev);
> + err = drmm_gem_shmem_init(ddev);
> + if (err < 0)
> + goto err_out2;
>
> return 0;
>
> +err_out2:
Let's stop this nonsense, and give err labels meaningful names
(err_unregister_dev for that one).
> + drm_dev_unregister(ddev);
> err_out1:
> pm_runtime_disable(pfdev->dev);
> panfrost_device_fini(pfdev);
> @@ -678,7 +672,6 @@ static void panfrost_remove(struct platform_device *pdev)
> struct drm_device *ddev = pfdev->ddev;
>
> drm_dev_unregister(ddev);
> - panfrost_gem_shrinker_cleanup(ddev);
>
> pm_runtime_get_sync(pfdev->dev);
> pm_runtime_disable(pfdev->dev);
> diff --git a/drivers/gpu/drm/panfrost/panfrost_gem.c b/drivers/gpu/drm/panfrost/panfrost_gem.c
> index bb9d43cf7c3c..a6128e32f303 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_gem.c
> +++ b/drivers/gpu/drm/panfrost/panfrost_gem.c
> @@ -19,16 +19,6 @@ static void panfrost_gem_free_object(struct drm_gem_object *obj)
> struct panfrost_gem_object *bo = to_panfrost_bo(obj);
> struct panfrost_device *pfdev = obj->dev->dev_private;
>
> - /*
> - * Make sure the BO is no longer inserted in the shrinker list before
> - * taking care of the destruction itself. If we don't do that we have a
> - * race condition between this function and what's done in
> - * panfrost_gem_shrinker_scan().
> - */
> - mutex_lock(&pfdev->shrinker_lock);
> - list_del_init(&bo->base.madv_list);
> - mutex_unlock(&pfdev->shrinker_lock);
> -
> /*
> * If we still have mappings attached to the BO, there's a problem in
> * our refcounting.
> @@ -94,7 +84,11 @@ static void panfrost_gem_mapping_release(struct kref *kref)
>
> mapping = container_of(kref, struct panfrost_gem_mapping, refcount);
>
> + /* shrinker that may purge mapping at the same time */
Let's give a detailed explanation here:
/* We need to do the unmapping with the resv lock held, because
* the shrinker might be purging mappings concurrently.
*/
> + dma_resv_lock(mapping->obj->base.base.resv, NULL);
This makes me think that maybe we could drop gem->mappings.lock and
protect the mappings list with the GEM resv. Not asking you to do that
in this patch though, it can be addressed in a follow-up.
> panfrost_gem_teardown_mapping(mapping);
> + dma_resv_unlock(mapping->obj->base.base.resv);
> +
> drm_gem_object_put(&mapping->obj->base.base);
> panfrost_mmu_ctx_put(mapping->mmu);
> kfree(mapping);
> @@ -228,6 +222,25 @@ static size_t panfrost_gem_rss(struct drm_gem_object *obj)
> return 0;
> }
>
> +static int panfrost_shmem_evict(struct drm_gem_object *obj)
> +{
> + struct panfrost_gem_object *bo = to_panfrost_bo(obj);
> +
> + if (!drm_gem_shmem_is_purgeable(&bo->base))
> + return -EBUSY;
> +
> + if (!mutex_trylock(&bo->mappings.lock))
> + return -EBUSY;
> +
> + panfrost_gem_teardown_mappings_locked(bo);
Okay, so I've modified and renamed
panfrost_gem_teardown_mappings_locked() here [1]. The new version is
called panfrost_gem_evict_mappings_locked(), and it just kills the MMU
mapping (with a panfrost_mmu_unmap() call). The mm_node (VA range) is
kept allocated until the panfrost_gem_mapping object is destroyed, which
better matches the eviction semantics IMHO.
> +
> + drm_gem_shmem_purge_locked(&bo->base);
> +
> + mutex_unlock(&bo->mappings.lock);
> +
> + return 0;
> +}
> +
> static const struct drm_gem_object_funcs panfrost_gem_funcs = {
> .free = panfrost_gem_free_object,
> .open = panfrost_gem_open,
> @@ -242,6 +255,7 @@ static const struct drm_gem_object_funcs panfrost_gem_funcs = {
> .status = panfrost_gem_status,
> .rss = panfrost_gem_rss,
> .vm_ops = &drm_gem_shmem_vm_ops,
> + .evict = panfrost_shmem_evict,
> };
>
> /**
> diff --git a/drivers/gpu/drm/panfrost/panfrost_gem.h b/drivers/gpu/drm/panfrost/panfrost_gem.h
> index 13c0a8149c3a..8ddc2d310d29 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_gem.h
> +++ b/drivers/gpu/drm/panfrost/panfrost_gem.h
> @@ -30,12 +30,6 @@ struct panfrost_gem_object {
> struct mutex lock;
> } mappings;
>
> - /*
> - * Count the number of jobs referencing this BO so we don't let the
> - * shrinker reclaim this object prematurely.
> - */
> - atomic_t gpu_usecount;
> -
> /*
> * Object chunk size currently mapped onto physical memory
> */
> @@ -86,7 +80,4 @@ panfrost_gem_mapping_get(struct panfrost_gem_object *bo,
> void panfrost_gem_mapping_put(struct panfrost_gem_mapping *mapping);
> void panfrost_gem_teardown_mappings_locked(struct panfrost_gem_object *bo);
>
> -void panfrost_gem_shrinker_init(struct drm_device *dev);
> -void panfrost_gem_shrinker_cleanup(struct drm_device *dev);
> -
> #endif /* __PANFROST_GEM_H__ */
> diff --git a/drivers/gpu/drm/panfrost/panfrost_gem_shrinker.c b/drivers/gpu/drm/panfrost/panfrost_gem_shrinker.c
> deleted file mode 100644
> index 1aa94fff7072..000000000000
> --- a/drivers/gpu/drm/panfrost/panfrost_gem_shrinker.c
> +++ /dev/null
> @@ -1,129 +0,0 @@
> -// SPDX-License-Identifier: GPL-2.0
> -/* Copyright (C) 2019 Arm Ltd.
> - *
> - * Based on msm_gem_freedreno.c:
> - * Copyright (C) 2016 Red Hat
> - * Author: Rob Clark <robdclark at gmail.com>
> - */
> -
> -#include <linux/list.h>
> -
> -#include <drm/drm_device.h>
> -#include <drm/drm_gem_shmem_helper.h>
> -
> -#include "panfrost_device.h"
> -#include "panfrost_gem.h"
> -#include "panfrost_mmu.h"
> -
> -static bool panfrost_gem_shmem_is_purgeable(struct drm_gem_shmem_object *shmem)
> -{
> - return (shmem->madv > 0) &&
> - !refcount_read(&shmem->pages_pin_count) && shmem->sgt &&
> - !shmem->base.dma_buf && !shmem->base.import_attach;
> -}
> -
> -static unsigned long
> -panfrost_gem_shrinker_count(struct shrinker *shrinker, struct shrink_control *sc)
> -{
> - struct panfrost_device *pfdev =
> - container_of(shrinker, struct panfrost_device, shrinker);
> - struct drm_gem_shmem_object *shmem;
> - unsigned long count = 0;
> -
> - if (!mutex_trylock(&pfdev->shrinker_lock))
> - return 0;
> -
> - list_for_each_entry(shmem, &pfdev->shrinker_list, madv_list) {
> - if (panfrost_gem_shmem_is_purgeable(shmem))
> - count += shmem->base.size >> PAGE_SHIFT;
> - }
> -
> - mutex_unlock(&pfdev->shrinker_lock);
> -
> - return count;
> -}
> -
> -static bool panfrost_gem_purge(struct drm_gem_object *obj)
> -{
> - struct drm_gem_shmem_object *shmem = to_drm_gem_shmem_obj(obj);
> - struct panfrost_gem_object *bo = to_panfrost_bo(obj);
> - bool ret = false;
> -
> - if (atomic_read(&bo->gpu_usecount))
> - return false;
> -
> - if (!mutex_trylock(&bo->mappings.lock))
> - return false;
> -
> - if (!dma_resv_trylock(shmem->base.resv))
> - goto unlock_mappings;
> -
> - panfrost_gem_teardown_mappings_locked(bo);
> - drm_gem_shmem_purge_locked(&bo->base);
> - ret = true;
> -
> - dma_resv_unlock(shmem->base.resv);
> -
> -unlock_mappings:
> - mutex_unlock(&bo->mappings.lock);
> - return ret;
> -}
> -
> -static unsigned long
> -panfrost_gem_shrinker_scan(struct shrinker *shrinker, struct shrink_control *sc)
> -{
> - struct panfrost_device *pfdev =
> - container_of(shrinker, struct panfrost_device, shrinker);
> - struct drm_gem_shmem_object *shmem, *tmp;
> - unsigned long freed = 0;
> -
> - if (!mutex_trylock(&pfdev->shrinker_lock))
> - return SHRINK_STOP;
> -
> - list_for_each_entry_safe(shmem, tmp, &pfdev->shrinker_list, madv_list) {
> - if (freed >= sc->nr_to_scan)
> - break;
> - if (drm_gem_shmem_is_purgeable(shmem) &&
> - panfrost_gem_purge(&shmem->base)) {
> - freed += shmem->base.size >> PAGE_SHIFT;
> - list_del_init(&shmem->madv_list);
> - }
> - }
> -
> - mutex_unlock(&pfdev->shrinker_lock);
> -
> - if (freed > 0)
> - pr_info_ratelimited("Purging %lu bytes\n", freed << PAGE_SHIFT);
> -
> - return freed;
> -}
> -
> -/**
> - * panfrost_gem_shrinker_init - Initialize panfrost shrinker
> - * @dev: DRM device
> - *
> - * This function registers and sets up the panfrost shrinker.
> - */
> -void panfrost_gem_shrinker_init(struct drm_device *dev)
> -{
> - struct panfrost_device *pfdev = dev->dev_private;
> - pfdev->shrinker.count_objects = panfrost_gem_shrinker_count;
> - pfdev->shrinker.scan_objects = panfrost_gem_shrinker_scan;
> - pfdev->shrinker.seeks = DEFAULT_SEEKS;
> - WARN_ON(register_shrinker(&pfdev->shrinker, "drm-panfrost"));
> -}
> -
> -/**
> - * panfrost_gem_shrinker_cleanup - Clean up panfrost shrinker
> - * @dev: DRM device
> - *
> - * This function unregisters the panfrost shrinker.
> - */
> -void panfrost_gem_shrinker_cleanup(struct drm_device *dev)
> -{
> - struct panfrost_device *pfdev = dev->dev_private;
> -
> - if (pfdev->shrinker.nr_deferred) {
> - unregister_shrinker(&pfdev->shrinker);
> - }
> -}
> diff --git a/drivers/gpu/drm/panfrost/panfrost_job.c b/drivers/gpu/drm/panfrost/panfrost_job.c
> index fb16de2d0420..da6be590557f 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_job.c
> +++ b/drivers/gpu/drm/panfrost/panfrost_job.c
> @@ -289,6 +289,19 @@ static void panfrost_attach_object_fences(struct drm_gem_object **bos,
> dma_resv_add_fence(bos[i]->resv, fence, DMA_RESV_USAGE_WRITE);
> }
>
> +static int panfrost_objects_prepare(struct drm_gem_object **bos, int bo_count)
> +{
> + struct panfrost_gem_object *bo;
> + int ret = 0;
> +
> + while (!ret && bo_count--) {
> + bo = to_panfrost_bo(bos[bo_count]);
> + ret = bo->base.madv ? -ENOMEM : 0;
That's more an -EINVAL: users are not supposed to pass BOs that have an
madv != WILL_NEED, if they do, that's their mistake, not a memory
allocation failure.
> + }
> +
> + return ret;
> +}
> +
> int panfrost_job_push(struct panfrost_job *job)
> {
> struct panfrost_device *pfdev = job->pfdev;
> @@ -300,6 +313,10 @@ int panfrost_job_push(struct panfrost_job *job)
> if (ret)
> return ret;
>
> + ret = panfrost_objects_prepare(job->bos, job->bo_count);
> + if (ret)
> + goto unlock;
> +
> mutex_lock(&pfdev->sched_lock);
> drm_sched_job_arm(&job->base);
>
> @@ -341,7 +358,6 @@ static void panfrost_job_cleanup(struct kref *ref)
> if (!job->mappings[i])
> break;
>
> - atomic_dec(&job->mappings[i]->obj->gpu_usecount);
> panfrost_gem_mapping_put(job->mappings[i]);
> }
> kvfree(job->mappings);
> diff --git a/drivers/gpu/drm/panfrost/panfrost_mmu.c b/drivers/gpu/drm/panfrost/panfrost_mmu.c
> index ac145a98377b..01cd97011ea5 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_mmu.c
> +++ b/drivers/gpu/drm/panfrost/panfrost_mmu.c
> @@ -326,6 +326,7 @@ int panfrost_mmu_map(struct panfrost_gem_mapping *mapping)
> struct panfrost_device *pfdev = to_panfrost_device(obj->dev);
> struct sg_table *sgt;
> int prot = IOMMU_READ | IOMMU_WRITE;
> + int ret = 0;
>
> if (WARN_ON(mapping->active))
> return 0;
> @@ -333,15 +334,26 @@ int panfrost_mmu_map(struct panfrost_gem_mapping *mapping)
> if (bo->noexec)
> prot |= IOMMU_NOEXEC;
>
> + if (!obj->import_attach) {
> + ret = drm_gem_shmem_pin(shmem);
I see why you do that. In practice panfrost_mmu_map() is called
before the object has been exposed, so I don't think it can be
purged/evicted at that point (and _get_pages() should have been called
before panfrost_mmu_map()), but I don't mind the extra safety net. Can
we just add a comment explaining the pin/get_pages_sgt/unpin dance here?
> + if (ret)
> + return ret;
> + }
> +
> sgt = drm_gem_shmem_get_pages_sgt(shmem);
> - if (WARN_ON(IS_ERR(sgt)))
> - return PTR_ERR(sgt);
> + if (WARN_ON(IS_ERR(sgt))) {
> + ret = PTR_ERR(sgt);
> + goto unpin;
> + }
>
> mmu_map_sg(pfdev, mapping->mmu, mapping->mmnode.start << PAGE_SHIFT,
> prot, sgt);
> mapping->active = true;
nit: add a blank line here, please.
> +unpin:
> + if (!obj->import_attach)
> + drm_gem_shmem_unpin(shmem);
>
> - return 0;
> + return ret;
> }
>
> void panfrost_mmu_unmap(struct panfrost_gem_mapping *mapping)
> diff --git a/include/drm/drm_gem_shmem_helper.h b/include/drm/drm_gem_shmem_helper.h
> index 6ac77c2082ed..2a506074da46 100644
> --- a/include/drm/drm_gem_shmem_helper.h
> +++ b/include/drm/drm_gem_shmem_helper.h
> @@ -61,13 +61,6 @@ struct drm_gem_shmem_object {
> */
> int madv;
>
> - /**
> - * @madv_list: List entry for madvise tracking
> - *
> - * Typically used by drivers to track purgeable objects
> - */
> - struct list_head madv_list;
> -
> /**
> * @sgt: Scatter/gather table for imported PRIME buffers
> */
[1]https://gitlab.freedesktop.org/bbrezillon/linux/-/commit/8401ba620de63073089517805f9413fac88653cd
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