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bh=fcOdDZPfT6Pc+nyQt0Z104yoPIvfvFyUOVPGZ/Hl6J8=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=J9dJXUx6JHtF3q5BB/WjISGMW5lPxnuFk0nEH2B49wVFYoeqEsS680fHiCOaqZdFW zZWMwAv6ACW5iTqH/WE86QUZlNQAQoVnWfntjdrbJTH/FT3KsrdDahe2uQB0889HRT N9vb15DRYNM2G8WVocMbJd3XN4Z22S+vPrTPr3IY= Date: Wed, 12 Apr 2023 13:13:02 -0700 From: Andrew Morton To: Pasha Tatashin Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, mike.kravetz@oracle.com, mhocko@suse.com, muchun.song@linux.dev, rientjes@google.com, souravpanda@google.com Subject: Re: [PATCH v2] mm: hugetlb_vmemmap: provide stronger vmemmap allocation guarantees Message-Id: <20230412131302.cf42a7f4b710db8c18b7b676@linux-foundation.org> In-Reply-To: <20230412195939.1242462-1-pasha.tatashin@soleen.com> References: <20230412195939.1242462-1-pasha.tatashin@soleen.com> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam03 X-Stat-Signature: cxw7kds3bn4hgh6ccpd17xja88uo4btq X-Rspamd-Queue-Id: E26CB4000A X-HE-Tag: 1681330384-416422 X-HE-Meta: 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 jVkXCcaO 9usMqTvrKo41oVz52BvRPUoeygTS+vZ3tbxMn3ov2j6enD3Pu4i6mk1EwOg2c4BuzjM4yS/XQCkA/Nf+d7mTfOYRseNDVh/W8x3MMqhY4ctEg9bi1n0+AXAJESGJ+T48PXmBmkNkNqARZeG1Wu1jfOThcXrAnSGHFNpqwjD1PdEmfMHLI4IbV/p0u39aIV64qZwd+JXpXBK+UY2qFl6y3SHq0eUOOb3l1DQuPYvhVPngXwf0H8fJlkHnFCuzeEgz5ec0z7eBhz0fefGHW+YniyQmGCKC+iewP4Lk5PAcd8/NiKXh6+fVdFfYwy+OMiRddHlOLH8GQXGiq7vdyPer+vEKdkCW4j0vMstIhiiN0/+sAn76z3V1x1j+JNsYoRTN44hk0TdXb/sfZE8aTMIdEJGrepS2h5EYzkUAzyf/HMg3meEUVCoT+O7GHc/p2NaGuYfto 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: Lots of questions (ie, missing information!) On Wed, 12 Apr 2023 19:59:39 +0000 Pasha Tatashin wrote: > HugeTLB pages have a struct page optimizations where struct pages for tail > pages are freed. However, when HugeTLB pages are destroyed, the memory for > struct pages (vmemmap) need to be allocated again. > > Currently, __GFP_NORETRY flag is used to allocate the memory for vmemmap, > but given that this flag makes very little effort to actually reclaim > memory the returning of huge pages back to the system can be problem. Are there any reports of this happening in the real world? > Lets > use __GFP_RETRY_MAYFAIL instead. This flag is also performs graceful > reclaim without causing ooms, but at least it may perform a few retries, > and will fail only when there is genuinely little amount of unused memory > in the system. If so, does this change help? If the allocation attempt fails, what are the consequences? What are the potential downsides to this change? Why did we choose __GFP_NORETRY in the first place? What happens if we try harder (eg, GFP_KERNEL)?