On Tue, 2024-12-03 at 17:39 +0100, Christian König wrote:
> Am 03.12.24 um 17:31 schrieb Thomas Hellström:
> > On Tue, 2024-12-03 at 17:20 +0100, Christian König wrote:
> > > [SNIP]
> > > > > > > > @@ -453,9 +601,36 @@ 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(t
> > > > > > > > t-
> > > > > > > > > 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;
> > > > > > > > + }
> > > > > > > Hui? Why is that part of the allocation function now?
> > > > > > >
> > > > > > > At bare minimum I would expect that this is a new
> > > > > > > function.
> > > > > > It's because we now have partially backed up tts, so the
> > > > > > restore is
> > > > > > interleaved on a per-page basis, replacing the backup
> > > > > > handles
> > > > > > with
> > > > > > page-pointers. I'll see if I can separate out at least the
> > > > > > initialization here.
> > > > > Yeah, that kind of makes sense.
> > > > >
> > > > > My expectation was just that we now have explicit
> > > > > ttm_pool_swapout()
> > > > > and
> > > > > ttm_pool_swapin() functions.
> > > > I fully understand, although in the allocation step, that would
> > > > also
> > > > increase the memory pressure since we might momentarily have
> > > > twice
> > > > the
> > > > bo-size allocated, if the shmem object was never swapped out,
> > > > and
> > > > we
> > > > don't want to unnecessarily risc OOM at recover time, although
> > > > that
> > > > should be a recoverable situation now. If the OOM receiver can
> > > > free
> > > > up
> > > > system memory resources they can could potentially restart the
> > > > recover.
> > > What I meant was more that we have ttm_pool_swapout() which does
> > > a
> > > mix
> > > of moving each page to a swap backend and freeing one by one.
> > >
> > > And ttm_pool_swapin() which allocates a bit of memory (usually
> > > one
> > > huge
> > > page) and then copies the content back in from the swap backend.
> > >
> > > Alternatively we could rename ttm_pool_alloc() into something
> > > like
> > > ttm_pool_populate() and ttm_pool_free() into
> > > ttm_pool_unpopulate(),
> > > but
> > > those names are not very descriptive either.
> > >
> > > It's just that we now do a bit more than just alloc and free in
> > > those
> > > functions, so the naming doesn't really match that well any more.
> > So what about ttm_pool_alloc() and ttm_pool_recover/swapin(), both
> > pointing to the same code, but _alloc() asserts that the tt isn't
> > backed up?
> >
> > That would give a clean interface at least.
>
> More or less ok. I would just put figuring out the gfp flags and the
> stuff inside the for (order... loop into separate functions. And then
> remove the if (tt->page_flags & TTM_TT_FLAG_PRIV_BACKED_UP) from the
> pool.
>
> In other words you trigger the back restore by calling a different
> function than the allocation one.
I'll take a look at this as well.
/Thomas
>
> >
> > For a renaming change that touch all TTM drivers, I'd rather put
> > that
> > as a last patch since getting acks for that from all TTM driver
> > maintainers seems like a hopeless undertaking.
>
> Yeah the acks are not the problem, merging it through the xe tree
> would be.
>
> Christian.
>
>
> >
> > /Thomas
> >
> >
> >
> >
> > > Christian.
> > >
> > > > /Thomas
>
