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[99.254.114.190]) by smtp.gmail.com with ESMTPSA id d75a77b69052e-466c4249f0asm41278911cf.81.2024.12.01.13.22.47 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 01 Dec 2024 13:22:49 -0800 (PST) From: Peter Xu To: linux-kernel@vger.kernel.org, linux-mm@kvack.org Cc: Rik van Riel , Breno Leitao , Andrew Morton , peterx@redhat.com, Muchun Song , Oscar Salvador , Roman Gushchin , Naoya Horiguchi , Ackerley Tng Subject: [PATCH 2/7] mm/hugetlb: Stop using avoid_reserve flag in fork() Date: Sun, 1 Dec 2024 16:22:35 -0500 Message-ID: <20241201212240.533824-3-peterx@redhat.com> X-Mailer: git-send-email 2.47.0 In-Reply-To: <20241201212240.533824-1-peterx@redhat.com> References: <20241201212240.533824-1-peterx@redhat.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" When fork() and stumble on top of a dma-pinned hugetlb private page, CoW must happen during fork() to guarantee dma coherency. In this specific path, hugetlb pages need to be allocated for the child process. Stop using avoid_reserve=3D1 flag here: it's not required to be used here, as dest_vma (which is destined to be a MAP_PRIVATE hugetlb vma) will have no private vma resv map, and that will make sure it won't be able to use a vma reservation later. No functional change intended with this change. Said that, it's still wanted to do this, so as to reduce the usage of avoid_reserve to the only one user, which is also why this flag was introduced initially in commit 04f2cbe35699 ("hugetlb: guarantee that COW faults for a process that called mmap(MAP_PRIVATE) on hugetlbfs will succeed"). I don't see whoever else should set it at all. Further patch will clean up resv accounting based on this. Signed-off-by: Peter Xu --- mm/hugetlb.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 9ce69fd22a01..8d4b4197d11b 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -5317,7 +5317,7 @@ int copy_hugetlb_page_range(struct mm_struct *dst, st= ruct mm_struct *src, spin_unlock(src_ptl); spin_unlock(dst_ptl); /* Do not use reserve as it's private owned */ - new_folio =3D alloc_hugetlb_folio(dst_vma, addr, 1); + new_folio =3D alloc_hugetlb_folio(dst_vma, addr, 0); if (IS_ERR(new_folio)) { folio_put(pte_folio); ret =3D PTR_ERR(new_folio); --=20 2.47.0