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Mon, 18 May 2026 11:10:39 -0700 (PDT) Received: from milan ([2001:9b1:d5a0:a500::24b]) by smtp.gmail.com with ESMTPSA id 2adb3069b0e04-5a9164cf003sm3427067e87.73.2026.05.18.11.10.38 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 18 May 2026 11:10:38 -0700 (PDT) From: Uladzislau Rezki X-Google-Original-From: Uladzislau Rezki Date: Mon, 18 May 2026 20:10:37 +0200 To: Shivam Kalra Cc: Andrew Morton , Shivam Kalra via B4 Relay , Uladzislau Rezki , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Alice Ryhl , Danilo Krummrich Subject: Re: [PATCH v13 0/5] mm/vmalloc: free unused pages on vrealloc() shrink Message-ID: References: <20260511-vmalloc-shrink-v13-0-643b7ec277a9@zohomail.in> <20260512150109.1a7939bb15f3d48ad866c540@linux-foundation.org> <8d678cb6-9f96-47b8-a25a-b3a969976630@zohomail.in> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <8d678cb6-9f96-47b8-a25a-b3a969976630@zohomail.in> X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 558B520007 X-Rspam-User: X-Stat-Signature: aiw4p5qm3j8qhu7w735un1ewhxygm7ee X-HE-Tag: 1779127841-512958 X-HE-Meta: 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 e4id3nyr C+uMYUomMXnWh7/AK30zNp6RLtrB54dzqIZVZTgFZ7MK9IB0wh8jLUm8Fc3sG9XTgSw5Ia1SYlFDsO82YfIAXln6/GFQWgJK7RwTN/T55gnmZGdEL5pZd3dM7IsgIuskT0zY0Snn8yz+xav3iG5kXutTY3GlC6BpUokwW6FU0z8UYAUQgASIoVVRtwqhTSR8f4AQGqDiNjqgqnogEa4zp9A9BzpY1o9hj1/3VW/vwu7XziwXuMLrP9u0N2qVptn8JT+bH4dHNGhMNaorUem1tov5legee1Ipa1AbyWPxa+MRx0Xgt/iSEnu01rtH+RSNpsda9APJNrviS8NKyykM0kDJf/w372nHGLQz3tH3xrIbH+89A4EqsFIJQKB30WtbrqnNrNorOfZrZPFs2Ce66JRGR7pdeO1Hoctrz/yp1viEzEJ/H/Gp45LO5G8ECj0WKmilLClLZRyKRqZCBri4g4S8+YxruZ46wVDFJxkL0m6w5Vy8P87jF/5U3iFxUeNp+FL2Qt8GZfkJqfqtmNMy12tvPfa2j8Wr/0atAovVjwosQpGVoRel9m4JQCKKERhl1Wgnsk8q/fL/xD2iJgnLl6BujDicmBt11WPgpMvXZPe/dleyrvsZz2zNyy79ri2q0Edt1zUK6dxL35i3VSmFqojc9NkxByIaYeTLd+hYn35VwKsp9QuM7IkEH8kAQV1FkQMTcL3kgO5Nc/9k= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, May 18, 2026 at 04:29:11AM +0530, Shivam Kalra wrote: > On 13/05/26 03:31, Andrew Morton wrote: > > On Mon, 11 May 2026 13:47:28 +0530 Shivam Kalra via B4 Relay wrote: > > > >> This series implements the TODO in vrealloc() to unmap and free unused > >> pages when shrinking across a page boundary. > > > > Thanks. AI review asked a few questions. Does anything here look > > legitimate? > > > > https://sashiko.dev/#/patchset/20260511-vmalloc-shrink-v13-0-643b7ec277a9@zohomail.in > > Thanks for flagging this. I went through the Sashiko review, and, > one of the findings is legitimate and needs a fix. > > 1) Patch 3 - vmap() mappings with nr_pages == 0 (LEGITIMATE) > This is correct. For vmap() areas created without VM_MAP_PUT_PAGES, > nr_pages is never set and stays 0 (vm_struct is kzalloc'd). With the > current patch, vread_iter() would compute size = 0 for these areas, > skip them entirely, and zero-fill the region in /proc/kcore. > > Ulad, this is the approach you suggested during v10 review [1]; we > both checked whether nr_pages could be 0 and concluded it couldn't, > but we only considered the VM_ALLOC (vmalloc) path. vmap() areas also > have vm != NULL but never set nr_pages unless VM_MAP_PUT_PAGES is > passed, which most callers don't use. > > Since vrealloc() only operates on VM_ALLOC areas, I think we can > scope the nr_pages path to just that: > if (vm) > /* > * For VM_ALLOC areas, use nr_pages rather than > * get_vm_area_size() because vrealloc() may shrink > * the mapping without updating area->size. Other > * mapping types (vmap, ioremap) don't set nr_pages. > */ > size = (vm->flags & VM_ALLOC) ? > (vm->nr_pages << PAGE_SHIFT) : > get_vm_area_size(vm); > else > size = va_size(va); > Ulad, does this approach look right to you, or would you prefer to > initialize nr_pages unconditionally in vmap() instead? > > [1] https://lore.kernel.org/lkml/aeYBYqPSEJRC8mjh@milan/ > Indeed, we missed that point regarding vmap() code. Checking VM_ALLOC sounds correct to me. -- Uladzislau Rezki