Ira Weiny <ira.weiny@xxxxxxxxx> writes:
> Ackerley Tng wrote:
>> Refactor out hugetlb_alloc_folio() from alloc_hugetlb_folio(), which
>> handles allocation of a folio and cgroup charging.
>>
>> Other than flags to control charging in the allocation process,
>> hugetlb_alloc_folio() also has parameters for memory policy.
>>
>> This refactoring as a whole decouples the hugetlb page allocation from
>> hugetlbfs, (1) where the subpool is stored at the fs mount, (2)
>> reservations are made during mmap and stored in the vma, and (3) mpol
>> must be stored at vma->vm_policy (4) a vma must be used for allocation
>> even if the pages are not meant to be used by host process.
>>
>> This decoupling will allow hugetlb_alloc_folio() to be used by
>> guest_memfd in later patches. In guest_memfd, (1) a subpool is created
>> per-fd and is stored on the inode, (2) no vma-related reservations are
>> used (3) mpol may not be associated with a vma since (4) for private
>> pages, the pages will not be mappable to userspace and hence have to
>> associated vmas.
>>
>> This could hopefully also open hugetlb up as a more generic source of
>> hugetlb pages that are not bound to hugetlbfs, with the complexities
>> of userspace/mmap/vma-related reservations contained just to
>> hugetlbfs.
>>
>> Signed-off-by: Ackerley Tng <ackerleytng@xxxxxxxxxx>
>> Change-Id: I60528f246341268acbf0ed5de7752ae2cacbef93
>> ---
>> include/linux/hugetlb.h | 12 +++
>> mm/hugetlb.c | 192 ++++++++++++++++++++++------------------
>> 2 files changed, 118 insertions(+), 86 deletions(-)
>>
>
> [snip]
>
>>
>> +/**
>> + * hugetlb_alloc_folio() - Allocates a hugetlb folio.
>> + *
>> + * @h: struct hstate to allocate from.
>> + * @mpol: struct mempolicy to apply for this folio allocation.
>> + * @ilx: Interleave index for interpretation of @mpol.
>> + * @charge_cgroup_rsvd: Set to true to charge cgroup reservation.
>> + * @use_existing_reservation: Set to true if this allocation should use an
>> + * existing hstate reservation.
>> + *
>> + * This function handles cgroup and global hstate reservations. VMA-related
>> + * reservations and subpool debiting must be handled by the caller if necessary.
>> + *
>> + * Return: folio on success or negated error otherwise.
>> + */
>> +struct folio *hugetlb_alloc_folio(struct hstate *h, struct mempolicy *mpol,
>> + pgoff_t ilx, bool charge_cgroup_rsvd,
>> + bool use_existing_reservation)
>> +{
>> + unsigned int nr_pages = pages_per_huge_page(h);
>> + struct hugetlb_cgroup *h_cg = NULL;
>> + struct folio *folio = NULL;
>> + nodemask_t *nodemask;
>> + gfp_t gfp_mask;
>> + int nid;
>> + int idx;
>> + int ret;
>> +
>> + idx = hstate_index(h);
>> +
>> + if (charge_cgroup_rsvd) {
>> + if (hugetlb_cgroup_charge_cgroup_rsvd(idx, nr_pages, &h_cg))
>> + goto out;
>
> Why not just return here?
> return ERR_PTR(-ENOSPC);
>
I wanted to consistently exit the function on errors at the same place,
and also make this refactoring look like I just took the middle of
alloc_hugetlb_folio() out as much as possible.
>> + }
>> +
>> + if (hugetlb_cgroup_charge_cgroup(idx, nr_pages, &h_cg))
>> + goto out_uncharge_cgroup_reservation;
>> +
>> + gfp_mask = htlb_alloc_mask(h);
>> + nid = policy_node_nodemask(mpol, gfp_mask, ilx, &nodemask);
>> +
>> + spin_lock_irq(&hugetlb_lock);
>> +
>> + if (use_existing_reservation || available_huge_pages(h))
>> + folio = dequeue_hugetlb_folio(h, gfp_mask, mpol, nid, nodemask);
>> +
>> + if (!folio) {
>> + spin_unlock_irq(&hugetlb_lock);
>> + folio = alloc_surplus_hugetlb_folio(h, gfp_mask, mpol, nid, nodemask);
>> + if (!folio)
>> + goto out_uncharge_cgroup;
>> + spin_lock_irq(&hugetlb_lock);
>> + list_add(&folio->lru, &h->hugepage_activelist);
>> + folio_ref_unfreeze(folio, 1);
>> + /* Fall through */
>> + }
>> +
>> + if (use_existing_reservation) {
>> + folio_set_hugetlb_restore_reserve(folio);
>> + h->resv_huge_pages--;
>> + }
>> +
>> + hugetlb_cgroup_commit_charge(idx, nr_pages, h_cg, folio);
>> +
>> + if (charge_cgroup_rsvd)
>> + hugetlb_cgroup_commit_charge_rsvd(idx, nr_pages, h_cg, folio);
>> +
>> + spin_unlock_irq(&hugetlb_lock);
>> +
>> + gfp_mask = htlb_alloc_mask(h) | __GFP_RETRY_MAYFAIL;
>> + ret = mem_cgroup_charge_hugetlb(folio, gfp_mask);
>> + /*
>> + * Unconditionally increment NR_HUGETLB here. If it turns out that
>> + * mem_cgroup_charge_hugetlb failed, then immediately free the page and
>> + * decrement NR_HUGETLB.
>> + */
>> + lruvec_stat_mod_folio(folio, NR_HUGETLB, pages_per_huge_page(h));
>> +
>> + if (ret == -ENOMEM) {
>> + free_huge_folio(folio);
>> + return ERR_PTR(-ENOMEM);
>> + }
>> +
>> + return folio;
>> +
>> +out_uncharge_cgroup:
>> + hugetlb_cgroup_uncharge_cgroup(idx, nr_pages, h_cg);
>> +out_uncharge_cgroup_reservation:
>> + if (charge_cgroup_rsvd)
>> + hugetlb_cgroup_uncharge_cgroup_rsvd(idx, nr_pages, h_cg);
>
> I find the direct copy of the unwind logic from alloc_hugetlb_folio()
> cumbersome and it seems like a good opportunity to clean it up.
>
I really wanted to make this refactoring look like I just took the
middle of alloc_hugetlb_folio() out as much as possible, to make it
obvious and understandable. I think the cleanup can be a separate patch
(series?)
>> +out:
>> + folio = ERR_PTR(-ENOSPC);
>> + goto out;
>
> Endless loop?
>
Thanks, this should have been
return folio;
> Ira
>
> [snip]
