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Shutemov" , Yang Shi , David Hildenbrand , Hugh Dickins , linux-kernel@vger.kernel.org Subject: Re: [PATCH v2] mm/khugepaged: skip shmem with userfaultfd Message-ID: References: <20230206112856.1802547-1-stevensd@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230206112856.1802547-1-stevensd@google.com> X-Rspamd-Queue-Id: E3F5A40007 X-Stat-Signature: 7iu741e7r5ny9k7fxj13s8r64s3u6sm7 X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1675693550-740093 X-HE-Meta: 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 6bG/+OgE LhEtBR91uHpLJkS+ljj4ly5YVXHcPBju71StsfXzeJ1yYsZeg0IboN7rne7f01bYbQHY/DVl5wQ6PUnngqmIzZZx+FOqBofuOq2V4HkYBOj8ELr70acXNBB2WQWNhxtkGReXdiXUH0Lg9LdUpDb6NkHr8Kw== 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: On Mon, Feb 06, 2023 at 08:28:56PM +0900, David Stevens wrote: > @@ -1747,6 +1748,7 @@ static int collapse_file(struct mm_struct *mm, unsigned long addr, > XA_STATE_ORDER(xas, &mapping->i_pages, start, HPAGE_PMD_ORDER); > int nr_none = 0, result = SCAN_SUCCEED; > bool is_shmem = shmem_file(file); > + bool i_mmap_locked = false; you don't need this ... > + * While iterating, we may drop the page cache lock multiple times. It > + * is safe to replace pages in the page cache with hpage while doing so > + * because nobody is able to map or otherwise access the content of > + * hpage until we unlock it. However, we cannot insert hpage into empty > + * indicies until we know we won't have to drop the page cache lock "indices". > @@ -1967,6 +1974,46 @@ static int collapse_file(struct mm_struct *mm, unsigned long addr, > put_page(page); > goto xa_unlocked; > } > + > + if (nr_none) { > + struct vm_area_struct *vma; > + int nr_none_check = 0; > + > + xas_unlock_irq(&xas); > + i_mmap_lock_read(mapping); > + i_mmap_locked = true; > + xas_lock_irq(&xas); > + > + xas_set(&xas, start); > + for (index = start; index < end; index++) { > + if (!xas_next(&xas)) > + nr_none_check++; > + } > + > + if (nr_none != nr_none_check) { > + result = SCAN_PAGE_FILLED; ... you can unlock the i_mmap_lock here before the goto. I think you need to add a case in madvise_collapse_errno(). It should probably return -EBUSY, I would think?