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Date: Thu, 9 Nov 2017 16:52:34 +0800 From: Miles Chen <miles.chen@...iatek.com> To: Christopher Lameter <cl@...ux.com> CC: Pekka Enberg <penberg@...nel.org>, David Rientjes <rientjes@...gle.com>, Joonsoo Kim <iamjoonsoo.kim@....com>, Andrew Morton <akpm@...ux-foundation.org>, <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>, <wsd_upstream@...iatek.com>, <linux-mediatek@...ts.infradead.org> Subject: Re: [PATCH] slub: Fix sysfs duplicate filename creation when slub_debug=O On Wed, 2017-11-08 at 09:05 -0600, Christopher Lameter wrote: > On Wed, 8 Nov 2017, Miles Chen wrote: > > > > Ok then the aliasing failed for some reason. The creation of the unique id > > > and the alias detection needs to be in sync otherwise duplicate filenames > > > are created. What is the difference there? > > > > The aliasing failed because find_mergeable() returns if (flags & > > SLAB_NEVER_MERGE) is true. So we do not go to search for alias caches. > > > > __kmem_cache_alias() > > find_mergeable() > > kmem_cache_flags() --> setup flag by the slub_debug > > if (flags & SLAB_NEVER_MERGE) return NULL; > > ... > > search alias logic... > > > > > > The flags maybe changed if disable_higher_order_debug=1. So the > > unmergeable cache becomes mergeable later. > > Ok so make sure taht the aliasing logic also clears those flags before > checking for SLAB_NEVER_MERGE. > > > > The clearing of the DEBUG_METADATA_FLAGS looks ok to me. kmem_cache_alias > > > should do the same right? > > > > > Yes, I think clearing DEBUG_METADATA flags in kmem_cache_alias is > > another solution for this issue. > > > > We will need to do calculate_sizes() by using original flags and compare > > the order of s->size and s->object_size when > > disable_higher_order_debug=1. > > Hmmm... Or move the aliasing check to a point where we know the size of > the slab objects? The biggest concern is that we may have some merged caches even if we enable CONFIG_SLUB_DEBUG_ON and slub_debug=O. So a developer cannot say "I set CONFIG_SLUB_DEBUG_ON=y to stop all slab merging". (https://www.spinics.net/lists/linux-mm/msg77919.html) In this fix patch, it disables slab merging if SLUB_DEBUG=O and CONFIG_SLUB_DEBUG_ON=y but the debug features are disabled by the disable_higher_order_debug logic and it holds the "slab merging is off if any debug features are enabled" behavior.
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