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Howlett" , Yun Zhou , Suren Baghdasaryan , Alex Sierra , Matthew Wilcox , Pasha Tatashin , Axel Rasmussen , "Gustavo A . R . Silva" , Dan Williams , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org, Greg KH , kernel@collabora.com, =?UTF-8?B?TWljaGHFgiBNaXJvc8WCYXc=?= Subject: Re: [PATCH v26 2/5] fs/proc/task_mmu: Implement IOCTL to get and optionally clear info about PTEs To: Andrei Vagin References: <20230727093637.1262110-1-usama.anjum@collabora.com> <20230727093637.1262110-3-usama.anjum@collabora.com> Content-Language: en-US From: Muhammad Usama Anjum In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: E1903140007 X-Stat-Signature: zd3jsb6w7i5kfumhqgwkhpgxd657bhmd X-HE-Tag: 1691382511-653333 X-HE-Meta: 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 qHeMJN9C FUtF3/W7rHPHevhBslSmT+X23e4XH0+uEg4VVKnM2KCs5CbJwuZiGsZ9Cr6vOZwPz9FhiNjnPGkHeJ1xpxnItgKdDok0wCnUZafXcHpSkNEduHCAAmogGmRU4pB+twMHohUDbq9hctgR9olTkOfxsMi6eAeNllXRziY/SHmMtvc/PEEBT4gStbpDa9q1If3pbRrsOx1VN5iwuHlDs1j4P2eGYvsA0NsNK8MydGsyjwMUjkmjGnJewzumKgk/kCcrvVUeS3JDKiOYoXUkohQn376uurNuUM95o35ye72Z0KOh6S6NV0p11I5RXPyy4Ueh1dMcfRKJnMgQEHc8= 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 8/5/23 2:53 AM, Andrei Vagin wrote: > On Thu, Jul 27, 2023 at 2:37 AM Muhammad Usama Anjum > wrote: >> > > > >> +static long do_pagemap_scan(struct mm_struct *mm, unsigned long uarg) >> +{ >> + unsigned long walk_start, walk_end; >> + struct mmu_notifier_range range; >> + struct pagemap_scan_private p; >> + size_t n_ranges_out = 0; >> + int ret; >> + >> + memset(&p, 0, sizeof(p)); >> + ret = pagemap_scan_get_args(&p.arg, uarg); >> + if (ret) >> + return ret; >> + >> + ret = pagemap_scan_init_bounce_buffer(&p); >> + if (ret) >> + return ret; >> + >> + /* Protection change for the range is going to happen. */ >> + if (p.arg.flags & PM_SCAN_WP_MATCHING) { >> + mmu_notifier_range_init(&range, MMU_NOTIFY_PROTECTION_VMA, 0, >> + mm, p.arg.start, p.arg.end); >> + mmu_notifier_invalidate_range_start(&range); >> + } >> + >> + walk_start = walk_end = p.arg.start; >> + for (; walk_end != p.arg.end; walk_start = walk_end) { >> + int n_out; >> + >> + walk_end = min_t(unsigned long, >> + (walk_start + PAGEMAP_WALK_SIZE) & PAGEMAP_WALK_MASK, >> + p.arg.end); > > This approach has performance implications. The basic program that scans > its address space takes around 20-30 seconds, but it has just a few > small mappings. The first optimization that comes to mind is to remove > the PAGEMAP_WALK_SIZE limit and instead halt walk_page_range when the > bounce buffer is full. After draining the buffer, the walk_page_range > function can be restarted. Yeah, I've this implemented in WIP and will be posting in next revision. > > The test program and perf data can be found here: > https://gist.github.com/avagin/c5a22f3c78f8cb34281602dfe9c43d10 > >> + >> + ret = mmap_read_lock_killable(mm); >> + if (ret) >> + break; >> + ret = walk_page_range(mm, walk_start, walk_end, >> + &pagemap_scan_ops, &p); >> + mmap_read_unlock(mm); >> + >> + n_out = pagemap_scan_flush_buffer(&p); >> + if (n_out < 0) >> + ret = n_out; >> + else >> + n_ranges_out += n_out; >> + >> + if (ret) >> + break; >> + } >> + > > Thanks, > Andrei -- BR, Muhammad Usama Anjum