[PATCH v8 2/6] drm/ttm/pool: Provide a helper to shrink pages
Thomas Hellström
thomas.hellstrom at linux.intel.com
Mon Aug 19 08:07:16 UTC 2024
Hi, Matt.
On Fri, 2024-08-16 at 14:10 +0000, Matthew Brost wrote:
> On Fri, Aug 16, 2024 at 03:37:13PM +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.
> > v8:
> > - Use a struct for flags for readability (Matt Brost)
> > - Address misc other review comments (Matt Brost)
> >
> > Cc: Christian König <christian.koenig at amd.com>
> > Cc: Somalapuram Amaranath <Amaranath.Somalapuram at amd.com>
> > Cc: Matthew Brost <matthew.brost at intel.com>
> > Cc: <dri-devel at lists.freedesktop.org>
> > Signed-off-by: Thomas Hellström <thomas.hellstrom at linux.intel.com>
> > ---
> > drivers/gpu/drm/ttm/ttm_pool.c | 394
> > +++++++++++++++++++++++++++++++--
> > drivers/gpu/drm/ttm/ttm_tt.c | 37 ++++
> > include/drm/ttm/ttm_pool.h | 6 +
> > include/drm/ttm/ttm_tt.h | 29 +++
> > 4 files changed, 453 insertions(+), 13 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/ttm/ttm_pool.c
> > b/drivers/gpu/drm/ttm/ttm_pool.c
> > index 8504dbe19c1a..0d224cd9f8eb 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 +598,36 @@ 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);
> > + 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 +644,19 @@ 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,
> > + ct
> > x);
> > + if (r)
> > + goto
> > error_free_all;
> > + }
> > +
> > if (num_pages < (1 << order))
> > break;
> >
> > @@ -496,9 +676,17 @@ 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 +705,26 @@ 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 +751,172 @@ 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.
> > + * @flags: Flags to govern the backup behaviour.
> > + *
> > + * 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,
> > + const struct ttm_backup_flags *flags)
> > +{
> > + 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() && !flags->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 || flags->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 (flags->purge) {
> > + shrunken += num_pages;
> > + page->private = 0;
> > + __free_pages(page, order);
> > + memset(ttm->pages + i, 0,
> > + num_pages * sizeof(*ttm-
> > >pages));
> > + }
> > + }
> > + }
> > +
> > + if (flags->purge)
> > + 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,
> > flags->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..f520b8c93f03 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 +159,8 @@ static void ttm_tt_init_fields(struct ttm_tt
> > *ttm,
> > ttm->swap_storage = NULL;
> > ttm->sg = bo->sg;
> > ttm->caching = caching;
> > + ttm->restore = NULL;
> > + ttm->backup = NULL;
> > }
> >
> > int ttm_tt_init(struct ttm_tt *ttm, struct ttm_buffer_object *bo,
> > @@ -182,6 +185,12 @@ 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) {
>
> Sorry for the conflicting comments in the last rev, but my last one
> here
> [1] regardind making this fully driver-owned didn’t receive a
> response.
> I’ll state it again: Do you think the backup fini should be owned by
> the
> driver? This would allow the driver to use a global backup for all TT
> if
> it wanted to. It would also make it consistent in the sense that the
> driver would own both the allocation and fini of the backup.
>
> Matt
>
> [1]
> https://patchwork.freedesktop.org/patch/602165/?series=131815&rev=6#comment_1104556
Sorry, I typed a lengthy reply to that comment but it somehow got lost.
Anyway, a single backup structure is, I think, possible with the
current implementation as well. In fact I use to have one of those
around for the direct-to-swap-cache implementation; basically the
backup_fini was a NOP IIRC.
One could also imagine the driver registering a large NVME file to use
for backup, In this each subclassed backup struct would probably want
to carry a refcount to the underlying file and each page position in
the file would be allocated using a struct ida or similar..
So for making it driver owned, I'm not completely following what you
mean. I noted in the docs that the driver needs to assign this value,
but thinking of it that should probably be done using the ttm_tt_init()
helper. Although that will require changing the ttm_tt_init() interface
for all drivers.
But if I missed the point, please get back. Meanwhile, I'm sending out
v9 with a couple of compilation fixes.
Thanks,
Thomas
>
> > + ttm->backup->ops->fini(ttm->backup);
> > + ttm->backup = NULL;
> > + }
> > +
> > if (ttm->pages)
> > kvfree(ttm->pages);
> > else
> > @@ -253,6 +262,34 @@ 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.
> > + * @flags: Flags that govern the backup behaviour.
> > + *
> > + * Update the page accounting and call ttm_pool_shrink_tt to free
> > pages
> > + * or back them up.
> > + *
> > + * 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,
> > + const struct ttm_backup_flags flags)
> > +{
> > + long ret;
> > +
> > + if (WARN_ON(IS_ERR_OR_NULL(tt->backup)))
> > + return 0;
> > +
> > + ret = ttm_pool_backup_tt(&bdev->pool, tt, &flags);
> > +
> > + if (ret > 0)
> > + tt->page_flags &= ~TTM_TT_FLAG_PRIV_POPULATED;
> > +
> > + return ret;
> > +}
> > +
> > /**
> > * 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..3112a4be835c 100644
> > --- a/include/drm/ttm/ttm_pool.h
> > +++ b/include/drm/ttm/ttm_pool.h
> > @@ -33,6 +33,7 @@
> >
> > struct device;
> > struct seq_file;
> > +struct ttm_backup_flags;
> > struct ttm_operation_ctx;
> > struct ttm_pool;
> > struct ttm_tt;
> > @@ -89,6 +90,11 @@ 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,
> > + const struct ttm_backup_flags *flags);
> > +
> > 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..e42a75cff502 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 +111,19 @@ 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.
> > + * Could be unified with @swap_storage. Meanwhile, this is
> > + * a driver-owned field.
> > + */
> > + 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. TTM
> > private */
> > + struct ttm_pool_tt_restore *restore;
> > };
> >
> > /**
> > @@ -230,6 +244,21 @@ 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);
> > +
> > +/**
> > + * struct ttm_backup_flags - Flags to govern backup behaviour.
> > + * @purge: Free pages without backing up. Bypass pools.
> > + * @writeback: Attempt to copy contents directly to swap space,
> > even
> > + * if that means blocking on writes to external memory.
> > + */
> > +struct ttm_backup_flags {
> > + u32 purge : 1;
> > + u32 writeback : 1;
> > +};
> > +
> > +long ttm_tt_backup(struct ttm_device *bdev, struct ttm_tt *tt,
> > + const struct ttm_backup_flags flags);
> > +
> > #if IS_ENABLED(CONFIG_AGP)
> > #include <linux/agp_backend.h>
> >
> > --
> > 2.44.0
> >
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