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Message-ID: <kpxl646zwhqcyrq23kfnslqdjgqy5s72vlq2uoc6vhfvwza2ld@yjyj3j6rnlag>
Date: Fri, 8 Nov 2024 14:42:48 -0800
From: Shakeel Butt <shakeel.butt@...ux.dev>
To: Joshua Hahn <joshua.hahnjy@...il.com>
Cc: hannes@...xchg.org, mhocko@...nel.org, roman.gushchin@...ux.dev,
muchun.song@...ux.dev, akpm@...ux-foundation.org, cgroups@...r.kernel.org,
linux-mm@...ck.org, linux-kernel@...r.kernel.org, kernel-team@...a.com
Subject: Re: [PATCH 2/3] memcg/hugetlb: Introduce mem_cgroup_charge_hugetlb
On Fri, Nov 08, 2024 at 01:29:45PM -0800, Joshua Hahn wrote:
> This patch introduces mem_cgroup_charge_hugetlb, which combines the
> logic of mem_cgroup{try,commit}_hugetlb. This reduces the footprint of
> memcg in hugetlb code, and also consolidates the error path that memcg
> can take into just one point.
>
> Signed-off-by: Joshua Hahn <joshua.hahnjy@...il.com>
>
> ---
> include/linux/memcontrol.h | 2 ++
> mm/hugetlb.c | 34 ++++++++++++----------------------
> mm/memcontrol.c | 19 +++++++++++++++++++
> 3 files changed, 33 insertions(+), 22 deletions(-)
>
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index bb49e0d4b377..d90c1ac791f1 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -678,6 +678,8 @@ static inline int mem_cgroup_charge(struct folio *folio, struct mm_struct *mm,
> int mem_cgroup_hugetlb_try_charge(struct mem_cgroup *memcg, gfp_t gfp,
> long nr_pages);
>
> +int mem_cgroup_charge_hugetlb(struct folio* folio, gfp_t gfp);
> +
> int mem_cgroup_swapin_charge_folio(struct folio *folio, struct mm_struct *mm,
> gfp_t gfp, swp_entry_t entry);
>
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index fbb10e52d7ea..6f6841483039 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -2967,21 +2967,13 @@ struct folio *alloc_hugetlb_folio(struct vm_area_struct *vma,
> struct hugepage_subpool *spool = subpool_vma(vma);
> struct hstate *h = hstate_vma(vma);
> struct folio *folio;
> - long map_chg, map_commit, nr_pages = pages_per_huge_page(h);
> + long map_chg, map_commit;
> long gbl_chg;
> - int memcg_charge_ret, ret, idx;
> + int ret, idx;
> struct hugetlb_cgroup *h_cg = NULL;
> - struct mem_cgroup *memcg;
> bool deferred_reserve;
> gfp_t gfp = htlb_alloc_mask(h) | __GFP_RETRY_MAYFAIL;
>
> - memcg = get_mem_cgroup_from_current();
> - memcg_charge_ret = mem_cgroup_hugetlb_try_charge(memcg, gfp, nr_pages);
> - if (memcg_charge_ret == -ENOMEM) {
> - mem_cgroup_put(memcg);
> - return ERR_PTR(-ENOMEM);
> - }
> -
> idx = hstate_index(h);
> /*
> * Examine the region/reserve map to determine if the process
> @@ -2989,12 +2981,8 @@ struct folio *alloc_hugetlb_folio(struct vm_area_struct *vma,
> * code of zero indicates a reservation exists (no change).
> */
> map_chg = gbl_chg = vma_needs_reservation(h, vma, addr);
> - if (map_chg < 0) {
> - if (!memcg_charge_ret)
> - mem_cgroup_cancel_charge(memcg, nr_pages);
> - mem_cgroup_put(memcg);
> + if (map_chg < 0)
> return ERR_PTR(-ENOMEM);
> - }
>
> /*
> * Processes that did not create the mapping will have no
> @@ -3092,10 +3080,15 @@ struct folio *alloc_hugetlb_folio(struct vm_area_struct *vma,
> }
> }
>
> - if (!memcg_charge_ret)
> - mem_cgroup_commit_charge(folio, memcg);
> - lruvec_stat_mod_folio(folio, NR_HUGETLB, pages_per_huge_page(h));
> - mem_cgroup_put(memcg);
> + ret = mem_cgroup_charge_hugetlb(folio, gfp);
> + if (ret == -ENOMEM) {
> + spin_unlock_irq(&hugetlb_lock);
spin_unlock_irq??
> + free_huge_folio(folio);
free_huge_folio() will call lruvec_stat_mod_folio() unconditionally but
you are only calling it on success. This may underflow the metric.
> + return ERR_PTR(-ENOMEM);
> + }
> + else if (!ret)
> + lruvec_stat_mod_folio(folio, NR_HUGETLB,
> + pages_per_huge_page(h));
>
> return folio;
>
> @@ -3110,9 +3103,6 @@ struct folio *alloc_hugetlb_folio(struct vm_area_struct *vma,
> hugepage_subpool_put_pages(spool, 1);
> out_end_reservation:
> vma_end_reservation(h, vma, addr);
> - if (!memcg_charge_ret)
> - mem_cgroup_cancel_charge(memcg, nr_pages);
> - mem_cgroup_put(memcg);
> return ERR_PTR(-ENOSPC);
> }
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 97f63ec9c9fb..95ee77fe27af 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -4529,6 +4529,25 @@ int mem_cgroup_hugetlb_try_charge(struct mem_cgroup *memcg, gfp_t gfp,
> return 0;
> }
>
> +int mem_cgroup_charge_hugetlb(struct folio *folio, gfp_t gfp)
> +{
> + struct mem_cgroup *memcg = get_mem_cgroup_from_current();
> + int ret = 0;
> +
> + if (mem_cgroup_disabled() || !memcg_accounts_hugetlb() ||
> + !memcg || !cgroup_subsys_on_dfl(memory_cgrp_subsys)) {
> + ret = -EOPNOTSUPP;
why EOPNOTSUPP? You need to return 0 here. We do want
lruvec_stat_mod_folio() to be called.
> + goto out;
> + }
> +
> + if (charge_memcg(folio, memcg, gfp))
> + ret = -ENOMEM;
> +
> +out:
> + mem_cgroup_put(memcg);
> + return ret;
> +}
> +
> /**
> * mem_cgroup_swapin_charge_folio - Charge a newly allocated folio for swapin.
> * @folio: folio to charge.
> --
> 2.43.5
>
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