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Date: Fri, 9 Dec 2016 02:00:17 +0000 From: Al Viro <viro@...IV.linux.org.uk> To: Dave Chinner <david@...morbit.com> Cc: Michal Hocko <mhocko@...nel.org>, linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>, Vlastimil Babka <vbabka@...e.cz>, David Rientjes <rientjes@...gle.com>, Mel Gorman <mgorman@...e.de>, Johannes Weiner <hannes@...xchg.org>, Anatoly Stepanov <astepanov@...udlinux.com>, LKML <linux-kernel@...r.kernel.org>, Michal Hocko <mhocko@...e.com>, Paolo Bonzini <pbonzini@...hat.com>, Mike Snitzer <snitzer@...hat.com>, dm-devel@...hat.com, "Michael S. Tsirkin" <mst@...hat.com>, Theodore Ts'o <tytso@....edu>, kvm@...r.kernel.org, linux-ext4@...r.kernel.org, linux-f2fs-devel@...ts.sourceforge.net, linux-security-module@...r.kernel.org Subject: Re: [RFC PATCH] mm: introduce kv[mz]alloc helpers On Fri, Dec 09, 2016 at 12:44:17PM +1100, Dave Chinner wrote: > On Thu, Dec 08, 2016 at 11:33:00AM +0100, Michal Hocko wrote: > > From: Michal Hocko <mhocko@...e.com> > > > > Using kmalloc with the vmalloc fallback for larger allocations is a > > common pattern in the kernel code. Yet we do not have any common helper > > for that and so users have invented their own helpers. Some of them are > > really creative when doing so. Let's just add kv[mz]alloc and make sure > > it is implemented properly. This implementation makes sure to not make > > a large memory pressure for > PAGE_SZE requests (__GFP_NORETRY) and also > > to not warn about allocation failures. This also rules out the OOM > > killer as the vmalloc is a more approapriate fallback than a disruptive > > user visible action. > > > > This patch also changes some existing users and removes helpers which > > are specific for them. In some cases this is not possible (e.g. > > ext4_kvmalloc, libcfs_kvzalloc, __aa_kvmalloc) because those seems to be > > broken and require GFP_NO{FS,IO} context which is not vmalloc compatible > > in general (note that the page table allocation is GFP_KERNEL). Those > > need to be fixed separately. > > See fs/xfs/kmem.c::kmem_zalloc_large(), which is XFS's version of > kvmalloc() that is GFP_NOFS/GFP_NOIO safe. Any generic API for this > functionality will have to play these memalloc_noio_save/ > memalloc_noio_restore games to ensure they are GFP_NOFS safe.... Easier to handle those in vmalloc() itself. The problem I have with these helpers is that different places have different cutoff thresholds for switch from kmalloc to vmalloc; has anyone done an analysis of those? -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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