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[90.233.215.147]) by smtp.gmail.com with ESMTPSA id 2adb3069b0e04-5a0eeb0b8f0sm2106563e87.14.2026.02.24.03.39.35 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 24 Feb 2026 03:39:36 -0800 (PST) From: Uladzislau Rezki X-Google-Original-From: Uladzislau Rezki Date: Tue, 24 Feb 2026 12:39:33 +0100 To: Michal Hocko , Mikulas Patocka Cc: Mikulas Patocka , "Vishal Moola (Oracle)" , Christoph Hellwig , "Uladzislau Rezki (Sony)" , SeongJae Park , Andrew Morton , zkabelac@redhat.com, Matthew Sakai , linux-mm@kvack.org, dm-devel@lists.linux.dev Subject: Re: [PATCH] mm: allow __GFP_RETRY_MAYFAIL in vmalloc Message-ID: References: <32bd9bed-a939-69c4-696d-f7f9a5fe31d8@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam09 X-Stat-Signature: dh77d39r7ycktohjtooreuwjt9itut9i X-Rspamd-Queue-Id: 3F60DC0008 X-Rspam-User: X-HE-Tag: 1771933178-696268 X-HE-Meta: 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 gNonzqF0 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 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: List-Subscribe: List-Unsubscribe: On Mon, Feb 23, 2026 at 11:08:02PM +0100, Michal Hocko wrote: > On Mon 23-02-26 20:25:38, Mikulas Patocka wrote: > > > > > > On Mon, 23 Feb 2026, Vishal Moola (Oracle) wrote: > > > > > On Thu, Feb 12, 2026 at 05:33:30PM +0100, Mikulas Patocka wrote: > > > > The commit 07003531e03c8 ("mm/vmalloc: warn on invalid vmalloc gfp > > > > flags") breaks the device mapper VDO target. The VDO target calls vmalloc > > > > with __GFP_RETRY_MAYFAIL and this flag is not in the mask of allowed > > > > flags. > > > > > > > > There is no reason why vmalloc couldn't support __GFP_RETRY_MAYFAIL, so > > > > let's add this flag to GFP_VMALLOC_SUPPORTED. > > > > > > My only skepticism about this comes from the line in the > > > vmalloc_node_range() doc: > > > "and %__GFP_RETRY_MAYFAIL are not supported." > > > > > > I myself don't know why that may be. Could you elaborate on if/why the > > > doc is wrong please? > > > > This statement was added by Michal Hocko in the commit > > b7d90e7a5ea8d64e668d5685925900d33d3884d5. Michal, could you explain why do > > you think that __GFP_RETRY_MAYFAIL is not supported? > > The problem with __GFP_RETRY_MAYFAIL is that it cannot be fully > supported. While pages that back the allocation can be easily made aware > of this failure mode there are page table allocations which are > hardocded GFP_KERNEL and there is no sensible way to extend the API to > change that (as we have learned several time over years). > > > The VDO module needs to allocate large amounts of memory and it doesn't > > want to trigger the OOM killer (which would kill some innocent task and > > wouldn't solve the out of memory condition at all), so I think that > > __GFP_RETRY_MAYFAIL is appropriate. > > Understood. But as said the very page table allocation could be the > trigger for the unwanted OOM. The same applies to __GFP_NORETRY > unfortunately as well. vmalloc has just recently gained support of > GFP_NOWAIT allocation mode, though. This will make the allocation > failure much more likely though so I am not entirely sure this is a > proper solution for your problem. > Yes, the page-table manipulation entries are hard-coded and it looks like it is the last path which is not wired properly with gfp-flags. Since we grow PTEs and never release it might not be a big issue for the __GFP_RETRY_MAYFAIL usage. But it is still not valid in noted path. -- Uladzislau Rezki