From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Morton Subject: + mm-clarify-__gfp_memalloc-usage.patch added to -mm tree Date: Fri, 03 Apr 2020 16:40:43 -0700 Message-ID: <20200403234043.lB0jbOUMQ%akpm@linux-foundation.org> References: <20200401210155.09e3b9742e1c6e732f5a7250@linux-foundation.org> Reply-To: linux-kernel@vger.kernel.org Return-path: Received: from mail.kernel.org ([198.145.29.99]:38432 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725268AbgDCXkp (ORCPT ); Fri, 3 Apr 2020 19:40:45 -0400 In-Reply-To: <20200401210155.09e3b9742e1c6e732f5a7250@linux-foundation.org> Sender: mm-commits-owner@vger.kernel.org List-Id: mm-commits@vger.kernel.org To: joel@joelfernandes.org, mhocko@suse.com, mm-commits@vger.kernel.org, neilb@suse.de, paulmck@kernel.org, rientjes@google.com The patch titled Subject: mm: clarify __GFP_MEMALLOC usage has been added to the -mm tree. Its filename is mm-clarify-__gfp_memalloc-usage.patch This patch should soon appear at http://ozlabs.org/~akpm/mmots/broken-out/mm-clarify-__gfp_memalloc-usage.patch and later at http://ozlabs.org/~akpm/mmotm/broken-out/mm-clarify-__gfp_memalloc-usage.patch Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** The -mm tree is included into linux-next and is updated there every 3-4 working days ------------------------------------------------------ From: Michal Hocko Subject: mm: clarify __GFP_MEMALLOC usage It seems that the existing documentation is not explicit about the expected usage and potential risks enough. While it is calls out that users have to free memory when using this flag it is not really apparent that users have to careful to not deplete memory reserves and that they should implement some sort of throttling wrt. freeing process. This is partly based on Neil's explanation [1]. [1] http://lkml.kernel.org/r/877dz0yxoa.fsf@notabene.neil.brown.name Link: http://lkml.kernel.org/r/20200403083543.11552-2-mhocko@kernel.org Signed-off-by: Michal Hocko Cc: David Rientjes Cc: Joel Fernandes Cc: Neil Brown Cc: Paul E. McKenney Signed-off-by: Andrew Morton --- include/linux/gfp.h | 3 +++ 1 file changed, 3 insertions(+) --- a/include/linux/gfp.h~mm-clarify-__gfp_memalloc-usage +++ a/include/linux/gfp.h @@ -110,6 +110,9 @@ struct vm_area_struct; * the caller guarantees the allocation will allow more memory to be freed * very shortly e.g. process exiting or swapping. Users either should * be the MM or co-ordinating closely with the VM (e.g. swap over NFS). + * Users of this flag have to be extremely careful to not deplete the reserve + * completely and implement a throttling mechanism which controls the consumption + * of the reserve based on the amount of freed memory. * * %__GFP_NOMEMALLOC is used to explicitly forbid access to emergency reserves. * This takes precedence over the %__GFP_MEMALLOC flag if both are set. _ Patches currently in -mm which might be from mhocko@suse.com are mm-clarify-__gfp_memalloc-usage.patch mm-make-it-clear-that-gfp-reclaim-modifiers-are-valid-only-for-sleepable-allocations.patch