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[90.233.217.11]) by smtp.gmail.com with ESMTPSA id 38308e7fff4ca-33238272944sm28012901fa.13.2025.08.08.06.12.47 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 08 Aug 2025 06:12:47 -0700 (PDT) From: Uladzislau Rezki X-Google-Original-From: Uladzislau Rezki Date: Fri, 8 Aug 2025 15:12:45 +0200 To: Michal Hocko Cc: "Uladzislau Rezki (Sony)" , linux-mm@kvack.org, Andrew Morton , Vlastimil Babka , Baoquan He , LKML Subject: Re: [PATCH 8/8] mm: Drop __GFP_DIRECT_RECLAIM flag if PF_MEMALLOC is set Message-ID: References: <20250807075810.358714-1-urezki@gmail.com> <20250807075810.358714-9-urezki@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Thu, Aug 07, 2025 at 01:58:20PM +0200, Michal Hocko wrote: > On Thu 07-08-25 09:58:10, Uladzislau Rezki wrote: > > The memory allocator already avoids reclaim when PF_MEMALLOC is set. > > Clear __GFP_DIRECT_RECLAIM explicitly to suppress might_alloc() warnings > > to make more correct behavior. > > Rather than chaning the gfp mask would it make more sense to update > might_alloc instead? > Hm.. I was thinking about it but decided to drop the __GFP_DIRECT_RECLAIM instead just to guarantee a no-reclaim behaviour, as it is written now to the flag. >From the other hand after this patch we would have some unneeded/dead checks(if i do not missing anything). For example: [1] WARN_ON_ONCE(!can_direct_reclaim); /* * PF_MEMALLOC request from this context is rather bizarre * because we cannot reclaim anything and only can loop waiting * for somebody to do a work for us. */ WARN_ON_ONCE(current->flags & PF_MEMALLOC); [2] /* no reclaim without waiting on it */ if (!(gfp_mask & __GFP_DIRECT_RECLAIM)) return false; /* this guy won't enter reclaim */ if (current->flags & PF_MEMALLOC) return false; [3] /* Caller is not willing to reclaim, we can't balance anything */ if (!can_direct_reclaim) goto nopage; /* Avoid recursion of direct reclaim */ if (current->flags & PF_MEMALLOC) goto nopage; etc. But, yes, might_alloc() can be modified also. -- Uladzislau Rezki