On Wed, Jul 03, 2024 at 05:38:10PM +0200, Thomas Hellström wrote:
> Provide a helper to shrink ttm_tt page-vectors on a per-page
> basis. A ttm_backup backend could then in theory get away with
> allocating a single temporary page for each struct ttm_tt.
>
> This is accomplished by splitting larger pages before trying to
> back them up.
>
> In the future we could allow ttm_backup to handle backing up
> large pages as well, but currently there's no benefit in
> doing that, since the shmem backup backend would have to
> split those anyway to avoid allocating too much temporary
> memory, and if the backend instead inserts pages into the
> swap-cache, those are split on reclaim by the core.
>
> Due to potential backup- and recover errors, allow partially swapped
> out struct ttm_tt's, although mark them as swapped out stopping them
> from being swapped out a second time. More details in the ttm_pool.c
> DOC section.
>
> v2:
> - A couple of cleanups and error fixes in ttm_pool_back_up_tt.
> - s/back_up/backup/
> - Add a writeback parameter to the exported interface.
>
> Cc: Christian König <christian.koe...@amd.com>
> Cc: Somalapuram Amaranath <amaranath.somalapu...@amd.com>
> Cc: Matthew Brost <matthew.br...@intel.com>
> Cc: <dri-devel@lists.freedesktop.org>
> Signed-off-by: Thomas Hellström <thomas.hellst...@linux.intel.com>
> ---
> drivers/gpu/drm/ttm/ttm_pool.c | 397 +++++++++++++++++++++++++++++++--
> drivers/gpu/drm/ttm/ttm_tt.c | 37 +++
> include/drm/ttm/ttm_pool.h | 5 +
> include/drm/ttm/ttm_tt.h | 20 ++
> 4 files changed, 446 insertions(+), 13 deletions(-)
>
> diff --git a/drivers/gpu/drm/ttm/ttm_pool.c b/drivers/gpu/drm/ttm/ttm_pool.c
> index 6e1fd6985ffc..38e50cf81b0a 100644
> --- a/drivers/gpu/drm/ttm/ttm_pool.c
> +++ b/drivers/gpu/drm/ttm/ttm_pool.c
> @@ -41,6 +41,7 @@
> #include <asm/set_memory.h>
> #endif
>
> +#include <drm/ttm/ttm_backup.h>
> #include <drm/ttm/ttm_pool.h>
> #include <drm/ttm/ttm_tt.h>
> #include <drm/ttm/ttm_bo.h>
> @@ -58,6 +59,32 @@ struct ttm_pool_dma {
> unsigned long vaddr;
> };
>
> +/**
> + * struct ttm_pool_tt_restore - State representing restore from backup
> + * @alloced_pages: Total number of already allocated pages for the ttm_tt.
> + * @restored_pages: Number of (sub) pages restored from swap for this
> + * chunk of 1 << @order pages.
> + * @first_page: The ttm page ptr representing for @old_pages[0].
> + * @caching_divide: Page pointer where subsequent pages are cached.
> + * @old_pages: Backup copy of page pointers that were replaced by the new
> + * page allocation.
> + * @pool: The pool used for page allocation while restoring.
> + * @order: The order of the last page allocated while restoring.
> + *
> + * Recovery from backup might fail when we've recovered less than the
> + * full ttm_tt. In order not to loose any data (yet), keep information
> + * around that allows us to restart a failed ttm backup recovery.
> + */
> +struct ttm_pool_tt_restore {
> + pgoff_t alloced_pages;
> + pgoff_t restored_pages;
> + struct page **first_page;
> + struct page **caching_divide;
> + struct ttm_pool *pool;
> + unsigned int order;
> + struct page *old_pages[];
> +};
> +
> static unsigned long page_pool_size;
>
> MODULE_PARM_DESC(page_pool_size, "Number of pages in the WC/UC/DMA pool");
> @@ -354,11 +381,102 @@ static unsigned int ttm_pool_page_order(struct
> ttm_pool *pool, struct page *p)
> return p->private;
> }
>
> +/*
> + * To be able to insert single pages into backup directly,
> + * we need to split multi-order page allocations and make them look
> + * like single-page allocations.
> + */
> +static void ttm_pool_split_for_swap(struct ttm_pool *pool, struct page *p)
> +{
> + unsigned int order = ttm_pool_page_order(pool, p);
> + pgoff_t nr;
> +
> + if (!order)
> + return;
> +
> + split_page(p, order);
> + nr = 1UL << order;
> + while (nr--)
> + (p++)->private = 0;
> +}
> +
> +/**
> + * DOC: Partial backup and restoration of a struct ttm_tt.
> + *
> + * Swapout using ttm_backup::ops::backup_page() and swapin using
> + * ttm_backup::ops::copy_backed_up_page() may fail.
> + * The former most likely due to lack of swap-space or memory, the latter due
> + * to lack of memory or because of signal interruption during waits.
> + *
> + * Backupfailure is easily handled by using a ttm_tt pages vector that holds
> + * both swap entries and page pointers. This has to be taken into account
> when
> + * restoring such a ttm_tt from backup, and when freeing it while backed up.
> + * When restoring, for simplicity, new pages are actually allocated from the
> + * pool and the contents of any old pages are copied in and then the old
> pages
> + * are released.
> + *
> + * For restoration failures, the struct ttm_pool_tt_restore holds sufficient
> state
> + * to be able to resume an interrupted restore, and that structure is freed
> once
> + * the restoration is complete. If the struct ttm_tt is destroyed while there
> + * is a valid struct ttm_pool_tt_restore attached, that is also properly
> taken
> + * care of.
> + */
> +
> +static bool ttm_pool_restore_valid(const struct ttm_pool_tt_restore *restore)
> +{
> + return restore && restore->restored_pages < (1 << restore->order);
> +}
> +
> +static int ttm_pool_restore_tt(struct ttm_pool_tt_restore *restore,
> + struct ttm_backup *backup,
> + struct ttm_operation_ctx *ctx)
> +{
> + unsigned int i, nr = 1 << restore->order;
> + int ret = 0;
> +
> + if (!ttm_pool_restore_valid(restore))
> + return 0;
> +
> + for (i = restore->restored_pages; i < nr; ++i) {
> + struct page *p = restore->old_pages[i];
> +
> + if (ttm_backup_page_ptr_is_handle(p)) {
> + unsigned long handle = ttm_backup_page_ptr_to_handle(p);
> +
> + if (handle == 0)
> + continue;
> +
> + ret = backup->ops->copy_backed_up_page
> + (backup, restore->first_page[i],
> + handle, ctx->interruptible);
> + if (ret)
> + break;
> +
> + backup->ops->drop(backup, handle);
> + } else if (p) {
> + /*
> + * We could probably avoid splitting the old page
> + * using clever logic, but ATM we don't care.
> + */
> + ttm_pool_split_for_swap(restore->pool, p);
> + copy_highpage(restore->first_page[i], p);
> + __free_pages(p, 0);
> + }
> +
> + restore->restored_pages++;
> + restore->old_pages[i] = NULL;
> + cond_resched();
> + }
> +
> + return ret;
> +}
> +
> /* Called when we got a page, either from a pool or newly allocated */
> static int ttm_pool_page_allocated(struct ttm_pool *pool, unsigned int order,
> struct page *p, dma_addr_t **dma_addr,
> unsigned long *num_pages,
> - struct page ***pages)
> + struct page ***pages,
> + struct ttm_pool_tt_restore *restore)
> {
> unsigned int i;
> int r;
> @@ -369,6 +487,16 @@ static int ttm_pool_page_allocated(struct ttm_pool
> *pool, unsigned int order,
> return r;
> }
>
> + if (restore) {
> + memcpy(restore->old_pages, *pages,
> + (1 << order) * sizeof(*restore->old_pages));
> + memset(*pages, 0, (1 << order) * sizeof(**pages));
> + restore->order = order;
> + restore->restored_pages = 0;
> + restore->first_page = *pages;
> + restore->alloced_pages += 1UL << order;
> + }
> +
> *num_pages -= 1 << order;
> for (i = 1 << order; i; --i, ++(*pages), ++p)
> **pages = p;
> @@ -394,22 +522,39 @@ static void ttm_pool_free_range(struct ttm_pool *pool,
> struct ttm_tt *tt,
> pgoff_t start_page, pgoff_t end_page)
> {
> struct page **pages = &tt->pages[start_page];
> + struct ttm_backup *backup = tt->backup;
> unsigned int order;
> pgoff_t i, nr;
>
> for (i = start_page; i < end_page; i += nr, pages += nr) {
> struct ttm_pool_type *pt = NULL;
> + struct page *p = *pages;
> +
> + if (ttm_backup_page_ptr_is_handle(p)) {
> + unsigned long handle = ttm_backup_page_ptr_to_handle(p);
> +
> + nr = 1;
> + if (handle != 0)
> + backup->ops->drop(backup, handle);
> + continue;
> + }
> +
> + if (pool) {
> + order = ttm_pool_page_order(pool, p);
> + nr = (1UL << order);
> + if (tt->dma_address)
> + ttm_pool_unmap(pool, tt->dma_address[i], nr);
>
> - order = ttm_pool_page_order(pool, *pages);
> - nr = (1UL << order);
> - if (tt->dma_address)
> - ttm_pool_unmap(pool, tt->dma_address[i], nr);
> + pt = ttm_pool_select_type(pool, caching, order);
> + } else {
> + order = p->private;
> + nr = (1UL << order);
> + }
>
> - pt = ttm_pool_select_type(pool, caching, order);
> if (pt)
> - ttm_pool_type_give(pt, *pages);
> + ttm_pool_type_give(pt, p);
> else
> - ttm_pool_free_page(pool, caching, order, *pages);
> + ttm_pool_free_page(pool, caching, order, p);
> }
> }
>
> @@ -453,9 +598,37 @@ int ttm_pool_alloc(struct ttm_pool *pool, struct ttm_tt
> *tt,
> else
> gfp_flags |= GFP_HIGHUSER;
>
> - for (order = min_t(unsigned int, MAX_PAGE_ORDER, __fls(num_pages));
> - num_pages;
> - order = min_t(unsigned int, order, __fls(num_pages))) {
> + order = min_t(unsigned int, MAX_PAGE_ORDER, __fls(num_pages));
> +
> + if (tt->page_flags & TTM_TT_FLAG_PRIV_BACKED_UP) {
> + if (!tt->restore) {
> + gfp_t gfp = GFP_KERNEL | __GFP_NOWARN;
> +
> + if (ctx->gfp_retry_mayfail)
> + gfp |= __GFP_RETRY_MAYFAIL;
> +
> + tt->restore =
> + kvzalloc(struct_size(tt->restore, old_pages,
> + (size_t)1 << order), gfp);
> + /* RFC: Possibly loop on -ENOMEM and reduce order. */
I'd say this is fine as is. If we can't allocate memory from an array of
pages here we likely pretty much screwed, right? e.g. We likely don't
have a chance of actually allocating new pages for the backing store
anyways. Also wouldn't the restart be broken if we can't fully track the
state of the restore?
> + if (!tt->restore)
> + return -ENOMEM;
> + } else if (ttm_pool_restore_valid(tt->restore)) {
> + struct ttm_pool_tt_restore *restore = tt->restore;
> +
> + num_pages -= restore->alloced_pages;
> + order = min_t(unsigned int, order, __fls(num_pages));
> + pages += restore->alloced_pages;
> + r = ttm_pool_restore_tt(restore, tt->backup, ctx);
> + if (r)
> + return r;
> + caching = restore->caching_divide;
> + }
> +
> + tt->restore->pool = pool;
> + }
> +
> + for (; num_pages; order = min_t(unsigned int, order, __fls(num_pages)))
> {
> struct ttm_pool_type *pt;
>
> page_caching = tt->caching;
> @@ -472,11 +645,19 @@ int ttm_pool_alloc(struct ttm_pool *pool, struct ttm_tt
> *tt,
> r = ttm_pool_page_allocated(pool, order, p,
> &dma_addr,
> &num_pages,
> - &pages);
> + &pages,
> + tt->restore);
> if (r)
> goto error_free_page;
>
> caching = pages;
> + if (ttm_pool_restore_valid(tt->restore)) {
> + r = ttm_pool_restore_tt(tt->restore,
> tt->backup,
> + ctx);
> + if (r)
> + goto error_free_all;
> + }
> +
> if (num_pages < (1 << order))
> break;
>
> @@ -496,9 +677,17 @@ int ttm_pool_alloc(struct ttm_pool *pool, struct ttm_tt
> *tt,
> caching = pages;
> }
> r = ttm_pool_page_allocated(pool, order, p, &dma_addr,
> - &num_pages, &pages);
> + &num_pages, &pages,
> + tt->restore);
> if (r)
> goto error_free_page;
> +
> + if (ttm_pool_restore_valid(tt->restore)) {
> + r = ttm_pool_restore_tt(tt->restore,
> tt->backup, ctx);
> + if (r)
> + goto error_free_all;
> + }
> +
> if (PageHighMem(p))
> caching = pages;
> }
> @@ -517,12 +706,26 @@ int ttm_pool_alloc(struct ttm_pool *pool, struct ttm_tt
> *tt,
> if (r)
> goto error_free_all;
>
> + if (tt->restore) {
> + kvfree(tt->restore);
> + tt->restore = NULL;
> + }
> +
> + if (tt->page_flags & TTM_TT_FLAG_PRIV_BACKED_UP)
> + tt->page_flags &= ~(TTM_TT_FLAG_PRIV_BACKED_UP |
> + TTM_TT_FLAG_SWAPPED);
> +
> return 0;
>
> error_free_page:
> ttm_pool_free_page(pool, page_caching, order, p);
>
> error_free_all:
> + if (tt->page_flags & TTM_TT_FLAG_PRIV_BACKED_UP) {
> + tt->restore->caching_divide = caching;
> + return r;
> + }
> +
> num_pages = tt->num_pages - num_pages;
> caching_divide = caching - tt->pages;
> ttm_pool_free_range(pool, tt, tt->caching, 0, caching_divide);
> @@ -549,6 +752,174 @@ void ttm_pool_free(struct ttm_pool *pool, struct ttm_tt
> *tt)
> }
> EXPORT_SYMBOL(ttm_pool_free);
>
> +/**
> + * ttm_pool_release_backed_up() - Release content of a swapped-out struct
> ttm_tt
> + * @tt: The struct ttm_tt.
> + *
> + * Release handles with associated content or any remaining pages of
> + * a backed-up struct ttm_tt.
> + */
> +void ttm_pool_release_backed_up(struct ttm_tt *tt)
> +{
> + struct ttm_backup *backup = tt->backup;
> + struct ttm_pool_tt_restore *restore;
> + pgoff_t i, start_page = 0;
> + unsigned long handle;
> +
> + if (!(tt->page_flags & TTM_TT_FLAG_PRIV_BACKED_UP))
> + return;
> +
> + restore = tt->restore;
> +
> + if (ttm_pool_restore_valid(restore)) {
> + pgoff_t nr = 1UL << restore->order;
> +
> + for (i = restore->restored_pages; i < nr; ++i) {
> + struct page *p = restore->old_pages[i];
> +
> + if (ttm_backup_page_ptr_is_handle(p)) {
> + handle = ttm_backup_page_ptr_to_handle(p);
> + if (handle == 0)
> + continue;
> +
> + backup->ops->drop(backup, handle);
> + } else if (p) {
> + ttm_pool_split_for_swap(restore->pool, p);
> + __free_pages(p, 0);
> + }
> + }
> + }
> +
> + if (restore) {
> + pgoff_t mid = restore->caching_divide - tt->pages;
> +
> + start_page = restore->alloced_pages;
> + /* Pages that might be dma-mapped and non-cached */
> + ttm_pool_free_range(restore->pool, tt, tt->caching,
> + 0, mid);
> + /* Pages that might be dma-mapped but cached */
> + ttm_pool_free_range(restore->pool, tt, ttm_cached,
> + mid, restore->alloced_pages);
> + }
> +
> + /* Shrunken pages. Cached and not dma-mapped. */
> + ttm_pool_free_range(NULL, tt, ttm_cached, start_page, tt->num_pages);
> +
> + if (restore) {
> + kvfree(restore);
> + tt->restore = NULL;
> + }
> +
> + tt->page_flags &= ~(TTM_TT_FLAG_PRIV_BACKED_UP | TTM_TT_FLAG_SWAPPED);
> +}
> +
> +/**
> + * ttm_pool_backup_tt() - Back up or purge a struct ttm_tt
> + * @pool: The pool used when allocating the struct ttm_tt.
> + * @ttm: The struct ttm_tt.
> + * @purge: Don't back up but release pages directly to system.
> + * @writeback: If !@purge, Try to write out directly to the
> + * underlying persistent media.
> + *
> + * Back up or purge a struct ttm_tt. If @purge is true, then
> + * all pages will be freed directly to the system rather than to the pool
> + * they were allocated from, making the function behave similarly to
> + * ttm_pool_free(). If @purge is false the pages will be backed up instead,
> + * exchanged for handles.
> + * A subsequent call to ttm_pool_alloc() will then read back the content and
> + * a subsequent call to ttm_pool_release_shrunken() will drop it.
> + * If backup of a page fails for whatever reason, @ttm will still be
> + * partially backed up, retaining those pages for which backup fails.
> + *
> + * Return: Number of pages actually backed up or freed, or negative
> + * error code on error.
> + */
> +long ttm_pool_backup_tt(struct ttm_pool *pool, struct ttm_tt *ttm, bool
> purge,
> + bool writeback)
> +{
> + struct ttm_backup *backup = ttm->backup;
> + struct page *page;
> + unsigned long handle;
> + gfp_t alloc_gfp;
> + gfp_t gfp;
> + int ret = 0;
> + pgoff_t shrunken = 0;
> + pgoff_t i, num_pages;
> +
> + if ((!get_nr_swap_pages() && !purge) ||
> + pool->use_dma_alloc ||
> + (ttm->page_flags & TTM_TT_FLAG_PRIV_BACKED_UP))
> + return -EBUSY;
> +
> +#ifdef CONFIG_X86
> + /* Anything returned to the system needs to be cached. */
> + if (ttm->caching != ttm_cached)
> + set_pages_array_wb(ttm->pages, ttm->num_pages);
> +#endif
> +
> + if (ttm->dma_address || purge) {
> + for (i = 0; i < ttm->num_pages; i += num_pages) {
> + unsigned int order;
> +
> + page = ttm->pages[i];
> + if (unlikely(!page)) {
> + num_pages = 1;
> + continue;
> + }
> +
> + order = ttm_pool_page_order(pool, page);
> + num_pages = 1UL << order;
> + if (ttm->dma_address)
> + ttm_pool_unmap(pool, ttm->dma_address[i],
> + num_pages);
> + if (purge) {
> + shrunken += num_pages;
> + page->private = 0;
> + __free_pages(page, order);
> + memset(ttm->pages + i, 0,
> + num_pages * sizeof(*ttm->pages));
> + }
> + }
> + }
> +
> + if (purge)
if (purge || !backup)?
> + return shrunken;
> +
> + if (pool->use_dma32)
> + gfp = GFP_DMA32;
> + else
> + gfp = GFP_HIGHUSER;
> +
> + alloc_gfp = GFP_KERNEL | __GFP_HIGH | __GFP_NOWARN |
> __GFP_RETRY_MAYFAIL;
> +
> + for (i = 0; i < ttm->num_pages; ++i) {
> + page = ttm->pages[i];
> + if (unlikely(!page))
> + continue;
> +
> + ttm_pool_split_for_swap(pool, page);
> +
> + handle = backup->ops->backup_page(backup, page, writeback, i,
> + gfp, alloc_gfp);
> + if (handle) {
> + ttm->pages[i] = ttm_backup_handle_to_page_ptr(handle);
> + put_page(page);
> + shrunken++;
> + } else {
> + /* We allow partially shrunken tts */
> + ret = -ENOMEM;
> + break;
> + }
> + cond_resched();
> + }
> +
> + if (shrunken)
> + ttm->page_flags |= (TTM_TT_FLAG_PRIV_BACKED_UP |
> + TTM_TT_FLAG_SWAPPED);
> +
> + return shrunken ? shrunken : ret;
> +}
> +
> /**
> * ttm_pool_init - Initialize a pool
> *
> diff --git a/drivers/gpu/drm/ttm/ttm_tt.c b/drivers/gpu/drm/ttm/ttm_tt.c
> index 4b51b9023126..98ce25197b38 100644
> --- a/drivers/gpu/drm/ttm/ttm_tt.c
> +++ b/drivers/gpu/drm/ttm/ttm_tt.c
> @@ -40,6 +40,7 @@
> #include <drm/drm_cache.h>
> #include <drm/drm_device.h>
> #include <drm/drm_util.h>
> +#include <drm/ttm/ttm_backup.h>
> #include <drm/ttm/ttm_bo.h>
> #include <drm/ttm/ttm_tt.h>
>
> @@ -158,6 +159,7 @@ static void ttm_tt_init_fields(struct ttm_tt *ttm,
> ttm->swap_storage = NULL;
> ttm->sg = bo->sg;
> ttm->caching = caching;
> + ttm->restore = NULL;
Set backup to NULL? Seems problematic if not set to NULL and driver
doesn't choose to set the backup.
> }
>
> int ttm_tt_init(struct ttm_tt *ttm, struct ttm_buffer_object *bo,
> @@ -182,6 +184,12 @@ void ttm_tt_fini(struct ttm_tt *ttm)
> fput(ttm->swap_storage);
> ttm->swap_storage = NULL;
>
> + ttm_pool_release_backed_up(ttm);
> + if (ttm->backup) {
In patch 12 you don't set this to NULL on error. You will have to set it
to NULL their or change this too:
if (ttm->backup && !IS_ERR(ttm->backup))
> + ttm->backup->ops->fini(ttm->backup);
> + ttm->backup = NULL;
> + }
> +
> if (ttm->pages)
> kvfree(ttm->pages);
> else
> @@ -253,6 +261,35 @@ int ttm_tt_swapin(struct ttm_tt *ttm)
> }
> EXPORT_SYMBOL_FOR_TESTS_ONLY(ttm_tt_swapin);
>
> +/**
> + * ttm_tt_backup() - Helper to back up a struct ttm_tt.
> + * @bdev: The TTM device.
> + * @tt: The struct ttm_tt.
> + * @purge: Don't back up but release pages directly to system,
> + * bypassing any pooling.
> + * @writeback: If !@purge, try to write out directly to the
> + * underlying persistent media.
> + *
> + * Helper for a TTM driver to use from the bo_shrink() method to shrink
> + * a struct ttm_tt, after it has done the necessary unbinding. This function
> + * will update the page accounting and call ttm_pool_shrink_tt to free pages
> + * or move them to the swap cache.
> + *
> + * Return: Number of pages freed or swapped out, or negative error code on
> + * error.
> + */
> +long ttm_tt_backup(struct ttm_device *bdev, struct ttm_tt *tt, bool purge,
> + bool writeback)
> +{
> + long ret = ttm_pool_backup_tt(&bdev->pool, tt, purge, writeback);
> +
> + if (ret > 0)
> + tt->page_flags &= ~TTM_TT_FLAG_PRIV_POPULATED;
> +
> + return ret;
> +}
> +EXPORT_SYMBOL(ttm_tt_backup);
> +
> /**
> * ttm_tt_swapout - swap out tt object
> *
> diff --git a/include/drm/ttm/ttm_pool.h b/include/drm/ttm/ttm_pool.h
> index 160d954a261e..4e4db369952b 100644
> --- a/include/drm/ttm/ttm_pool.h
> +++ b/include/drm/ttm/ttm_pool.h
> @@ -89,6 +89,11 @@ void ttm_pool_fini(struct ttm_pool *pool);
>
> int ttm_pool_debugfs(struct ttm_pool *pool, struct seq_file *m);
>
> +void ttm_pool_release_backed_up(struct ttm_tt *tt);
> +
> +long ttm_pool_backup_tt(struct ttm_pool *pool, struct ttm_tt *ttm,
> + bool purge, bool writeback);
> +
> int ttm_pool_mgr_init(unsigned long num_pages);
> void ttm_pool_mgr_fini(void);
>
> diff --git a/include/drm/ttm/ttm_tt.h b/include/drm/ttm/ttm_tt.h
> index 2b9d856ff388..6b990f1e7dd0 100644
> --- a/include/drm/ttm/ttm_tt.h
> +++ b/include/drm/ttm/ttm_tt.h
> @@ -32,11 +32,13 @@
> #include <drm/ttm/ttm_caching.h>
> #include <drm/ttm/ttm_kmap_iter.h>
>
> +struct ttm_backup;
> struct ttm_device;
> struct ttm_tt;
> struct ttm_resource;
> struct ttm_buffer_object;
> struct ttm_operation_ctx;
> +struct ttm_pool_tt_restore;
>
> /**
> * struct ttm_tt - This is a structure holding the pages, caching- and
> aperture
> @@ -85,6 +87,9 @@ struct ttm_tt {
> * fault handling abuses the DMA api a bit and dma_map_attrs can't be
> * used to assure pgprot always matches.
> *
> + * TTM_TT_FLAG_PRIV_BACKED_UP: TTM internal only. This is set if the
> + * struct ttm_tt has been (possibly partially) backed up.
> + *
> * TTM_TT_FLAG_PRIV_POPULATED: TTM internal only. DO NOT USE. This is
> * set by TTM after ttm_tt_populate() has successfully returned, and is
> * then unset when TTM calls ttm_tt_unpopulate().
> @@ -96,6 +101,7 @@ struct ttm_tt {
> #define TTM_TT_FLAG_DECRYPTED BIT(4)
>
> #define TTM_TT_FLAG_PRIV_POPULATED BIT(5)
> +#define TTM_TT_FLAG_PRIV_BACKED_UP BIT(6)
> uint32_t page_flags;
> /** @num_pages: Number of pages in the page array. */
> uint32_t num_pages;
> @@ -105,11 +111,21 @@ struct ttm_tt {
> dma_addr_t *dma_address;
> /** @swap_storage: Pointer to shmem struct file for swap storage. */
> struct file *swap_storage;
> + /**
> + * @backup: Pointer to backup struct for backed up tts.
> + * RFC: Could possibly be unified with @swap_storage.
I think longterm unifying with swap_storage is problably a good idea.
Kinda goofy having two backup mechanisms.
In the meantime, can you add a comment that is this is a driver owned
field? This confused me until I looked at the last patch in this series
where this field was being setup.
> + */
> + struct ttm_backup *backup;
> /**
> * @caching: The current caching state of the pages, see enum
> * ttm_caching.
> */
> enum ttm_caching caching;
> + /**
> + * @restore: Partial restoration from backup state.
> + * RFC: Incorporate in struct ttm_backup?
I think having a standalone restore field makes sense. Also probably
mention is this a TTM private field and drivers shouldn't touch this.
Matt
> + */
> + struct ttm_pool_tt_restore *restore;
> };
>
> /**
> @@ -230,6 +246,10 @@ 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);
> unsigned long ttm_tt_pages_limit(void);
> +
> +long ttm_tt_backup(struct ttm_device *bdev, struct ttm_tt *tt, bool purge,
> + bool writeback);
> +
> #if IS_ENABLED(CONFIG_AGP)
> #include <linux/agp_backend.h>
>
> --
> 2.44.0
>
