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Tue, 20 Dec 2022 04:42:09 -0800 (PST) Date: Tue, 20 Dec 2022 12:42:09 +0000 From: Lorenzo Stoakes To: Baoquan He Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, urezki@gmail.com, stephen.s.brennan@oracle.com, willy@infradead.org, akpm@linux-foundation.org, hch@infradead.org Subject: Re: [PATCH v2 2/7] mm/vmalloc.c: add flags to mark vm_map_ram area Message-ID: References: <20221217015435.73889-1-bhe@redhat.com> <20221217015435.73889-3-bhe@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Queue-Id: 5CDBC10000A X-Stat-Signature: wcmea7e5axjhn4czmaezobqw39uep7ht X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1671540132-275278 X-HE-Meta: U2FsdGVkX1+yryexe8GxilaCP904Kc37oCw5O59zZP/zqHDGeQaHFTiTqd1hac9AzL9tWwla+i9GN/7e5zndo9LrhE5/soZ9UaIUWifgqwULViVU01CVmKZa+BM/Ii00j58XmEutoWOxMZ67UV5081uVoxuVt714I46N62NNsl9auhq6f8BhqHt6r7B21W7GU3J1E9IC/jAhNUBf26QRhGCNOuii5euz5Gj5Cw9mpa9OkvqH8zzVlpKy/Ao+OkXaIPe82Px5DgSKN4Y414agHlNfXWots403wvaWJ+jWewSrpt099zUWMubGKbAXHKzc4VinGt1W2V1xnVL9BwDP1HVlVB27UiYdrA45zlC53RcA2qESlrw2/30u3lRtEOFoeEx2ymkvUwXvaryq5+ovohqyLAGPKhwK1CpcyDLbFVRiOJG51TWuF66aH8E4cB+kD/zOX0MZ8Mi/vHmmOAsHLclAUa+yE32pzy636FNHuedRk0sZJk5hVGsyVJW5luTfVILxyZHu/RYZRoIo9UqzD3M5/NcEVyCkuplaN2ys8q8gxWUeFb5qLcrNhRAqz9hqOBZsWWB0WuaUSDVIckeFjTfjxMTq9GPrMGJzzg1bFyz9ManRNjcO3Cu24Gf+GNt00gF/ovx3EtvRQ0fZ0i3jdAtM9NOm/zrsh7POwJVzdUf/TCJZzHCp6Sk47Ety7CMPvwpcnNymT+yt4cd36tC6KKM2p9mbIsbleF0J/cDx/we1pYO6fbZIcW6RX3ezWiqAAW+nsvLsrtlQxzuZw8d3NLcT3ZwlauXi2tQB+m3PC9VvNTqJ1PgcQBTlkHbMAaJh5yY9ixOY5uk/txM/A70zpvMdK1H7GP21HUZ84fN34VWQ+EHTz3dYZfJve961qGwe3FHhFaelqJLMgp3MgK3briVv2e8Y2ScAMOG2Dr1xjybV7afUNh1E3KO4WH8p1c2hDgXF1fR6nFI47Kb/UZM T/Xjolac ZodtP/540zc1XJcZf/WkU435CxYLNMSZ7PBGTD3291PoogWf4ON+MT97KUlJMuZ43Qj08+aaiH0uapl7YtQp0l8btpDW4ChB6synQopqW7/xwO/rM2UcpHFAt4JeXh0PBZ1xq 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 Tue, Dec 20, 2022 at 08:14:15PM +0800, Baoquan He wrote: > Hmm, for the two kinds of vm_map_ram areas, their code paths are > different. for unmapping vmap_block vm_map_ram, it goes through > vb_free(). I can only do the clearing in free_vmap_block(). > > -->vm_unmap_ram() > -->vb_free() > -->free_vmap_block() > > For non vmap_block vm_map_ram area, I can do the clearing in > vm_unmap_ram(). > -->vm_unmap_ram() > -->__find_vmap_area() > -->free_unmap_vmap_area() > > As said earlier, clearing va->flags when unmap vm_map_ram area, or > clearing va->vm in remove_vm_area(), these have better be done. > However, not clearing them won't cause issue currently. Because the > old vmap_area is inserted into free_vmap_area_root, when we allocate a > new vmap_area through alloc_vmap_area(), we will get q new vmap_area > from vmap_area_cachep, the old va->flags or va->vm won't be carried into > the new vmap_area. Clearing them is a good to have, just in case. > Sure, this is more so about avoiding confusion and perhaps some future change which might not take into account that flag state could be invalid. I guess logically speaking, this is still a block when you are unmapping ram, so it's not unreasonable to retain the VMAP_BLOCK flag. In that case I'd say we're good simply clearing VMAP_RAM here. Thanks for the explanations! > Rethinking about this, I may need to do the clearing when freeing > vmap_block. Otherwise, people will be confused why the clearing is not > done. > > @@ -1815,6 +1815,7 @@ static void free_vmap_area_noflush(struct vmap_area *va) > > spin_lock(&vmap_area_lock); > unlink_va(va, &vmap_area_root); > + va->flags = 0; > spin_unlock(&vmap_area_lock); > > nr_lazy = atomic_long_add_return((va->va_end - va->va_start) >> > That sounds like a good idea!