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Wed, 6 Nov 2024 10:13:11 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id +lXnAzdBK2ftYQAAD6G6ig (envelope-from ); Wed, 06 Nov 2024 10:13:11 +0000 Date: Wed, 6 Nov 2024 11:13:09 +0100 From: Oscar Salvador To: Ackerley Tng Cc: muchun.song@linux.dev, peterx@redhat.com, akpm@linux-foundation.org, rientjes@google.com, fvdl@google.com, jthoughton@google.com, david@redhat.com, isaku.yamahata@intel.com, zhiquan1.li@intel.com, fan.du@intel.com, jun.miao@intel.com, tabba@google.com, quic_eberman@quicinc.com, roypat@amazon.co.uk, jgg@nvidia.com, jhubbard@nvidia.com, seanjc@google.com, pbonzini@redhat.com, erdemaktas@google.com, vannapurve@google.com, pgonda@google.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [RFC PATCH 1/3] mm: hugetlb: Simplify logic in dequeue_hugetlb_folio_vma() Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Action: no action X-Rspamd-Queue-Id: 0367020006 X-Stat-Signature: sqxkxuck954ua7nufj8dtj3raxnys1c4 X-Rspam-User: X-Rspamd-Server: rspam05 X-HE-Tag: 1730887958-603135 X-HE-Meta: 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 89e4Pi/v kmHNlB+nqrTnmKIzlrP7eYHBDiu1X67Mdh1t0cTG9BQQIqkkkA7waasOCcQTsgx66pL4Wfbz4L2ygrXR/q2e7ZJPjof2r+mkh0zPhL35PGSAO0zUoqW8FtsREDbgr5BBW8C+6pGTk0lB0rW7scpxmW9gouoVov3UOoAzB6c+N43/1/+4DHCxd9RPZ4xFLI1VwxqBR/Eul1oW0H1ryMlbi7YQlzQcH7UrZaz6VNgscSKe3RBbZTj5fJL896Ivvq0BYcLqQHUMbxrvqSYWxzX5SlUW0ZcvYe5D51BHEUpwOoli0Lzqdhf05WpA6jpUrD23IzC7m4u8Cn/Mk7lsxDaKLEdkcQA== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, Oct 11, 2024 at 11:22:36PM +0000, Ackerley Tng wrote: > Replace arguments avoid_reserve and chg in dequeue_hugetlb_folio_vma() > so dequeue_hugetlb_folio_vma() is more understandable. > > The new argument, use_hstate_resv, indicates whether the folio to be > dequeued should be taken from reservations in hstate. > > If use_hstate_resv is true, the folio to be dequeued should be taken > from reservations in hstate and hence h->resv_huge_pages is > decremented, and the folio is marked so that the reservation is > restored. > > If use_hstate_resv is false, then a folio needs to be taken from the > pool and hence there must exist available_huge_pages(h), failing > which, goto err. > > The bool use_hstate_resv can be reused within > dequeue_hugetlb_folio_vma()'s caller, alloc_hugetlb_folio(). > > No functional changes are intended. > > As proof, the original two if conditions > > !vma_has_reserves(vma, chg) && !available_huge_pages(h) > > and > > avoid_reserve && !available_huge_pages(h) > > can be combined into > > (avoid_reserve || !vma_has_reserves(vma, chg)) > && !available_huge_pages(h). > > Applying de Morgan's theorem on > > avoid_reserve || !vma_has_reserves(vma, chg) > > yields > > !avoid_reserve && vma_has_reserves(vma, chg), > > hence the simplification is correct. > > Signed-off-by: Ackerley Tng I like this, it is a nice simplification and hugetlb revervation mechanism is already hard enough to follow. As already mentioned, Sean's changes look easier to follow. Reviewed-by: Oscar Salvador On a side note, we might want to convert the 'avoid_reserve' param from alloc_hugetlb_folio into a bool, as we are using it exactly like that, so it would seem more natutal. > --- > mm/hugetlb.c | 33 +++++++++++---------------------- > 1 file changed, 11 insertions(+), 22 deletions(-) > > diff --git a/mm/hugetlb.c b/mm/hugetlb.c > index 190fa05635f4..73165c670739 100644 > --- a/mm/hugetlb.c > +++ b/mm/hugetlb.c > @@ -1281,8 +1281,9 @@ static bool vma_has_reserves(struct vm_area_struct *vma, long chg) > } > > /* > - * Only the process that called mmap() has reserves for > - * private mappings. > + * Only the process that called mmap() has reserves for private > + * mappings. A child process with MAP_PRIVATE mappings created by their > + * parent have no page reserves. 'page reserves' looks odd. I would say 'reservations'. -- Oscar Salvador SUSE Labs