From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 325D4442FB8; Tue, 21 Jul 2026 10:07:39 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784628460; cv=none; b=jUdGhQeU9Xt3cpU/PIBw+9y+EbpXzu/UjO5wfkiSMYQrIIa9hlG3J/zGnq2f5lTGZ3CeHPMLras9SoF4wTaqBKICIPOu97lcKaEdZf+14YFX+5DfhOYQxXcBUi9COob5jyMr1W4GEEl0wXfj6AKURhdFYGI7FkC2lrDgzDvOHFQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784628460; c=relaxed/simple; bh=EX86EBA1Lpd+L1z2KYaIjSNr/t3YbxGeFxCyt+vkhvg=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=PXe2/T485H+AtQX/1M6t93GOrwJyjsZ2eefhYRc6/ln4IPmTrcofSlxhBAOPUtdDkBy5KaW/UM2W9U3SZMfg4f8eHNjw1zXqfl8ceR3oK5g9YItHhiTogH9OibkkiDWtHQMFgWVZ6S3tH6GVYdGOedYlqZjLyeMxHB0PEa3OcCc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=c+XgjAmg; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="c+XgjAmg" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1722B1F00A3A; Tue, 21 Jul 2026 10:07:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1784628459; bh=bOploRvDj134COovQFMYbavpqHjEd7HZWn3WCljAxGI=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=c+XgjAmgGbN4YGbGofBEf6QaJ4+OzyF+uyxW5Lbiu/b+Bx+Ghw3EBQVy0+a7ELCCb KTsigTcX0kRsAvMAqfvxWiPJgpY60F1DapyGEjHQRP7X9sNyGcZiPXblyvPPSBhmhd X8wQqDUCZ4DmpA3F0xyh6ZkZV9hDD3uhfVJt7ZWH3VDiiS/v9O99GVzR0k4XRkJWjz RsoySu/eKwL7XgFbm0ImUaXEzXgHmnBtcN/DlCewPNrLbUzJtbNfQ0byWKxvA8qON+ SOxMmrYn5KUO76dtdAHxN3Oetv9ktGLMJ5+vvgPNumGe7OQWVzkf3NjGOHoKsauDbT Vtm/bXBdlk+UA== Message-ID: <1d0d8021-62d2-4c42-a2a6-a7e8ce2f5d37@kernel.org> Date: Tue, 21 Jul 2026 12:07:31 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH slab/for-next v4 2/8] mm/slab: handle the !allow_spin case in kfree_rcu_sheaf() Content-Language: en-US To: "Harry Yoo (Oracle)" , Andrew Morton , Hao Li , Christoph Lameter , David Rientjes , Roman Gushchin , Alexei Starovoitov , Andrii Nakryiko , Puranjay Mohan , Amery Hung , Sebastian Andrzej Siewior , Clark Williams , Steven Rostedt , "Paul E. McKenney" , Frederic Weisbecker , Neeraj Upadhyay , Joel Fernandes , Josh Triplett , Boqun Feng , Uladzislau Rezki , Mathieu Desnoyers , Lai Jiangshan , Zqiang , Pedro Falcato , Suren Baghdasaryan , Shengming Hu Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-rt-devel@lists.linux.dev, rcu@vger.kernel.org, bpf@vger.kernel.org References: <20260720-kfree_rcu_nolock-v4-0-964e03c41a4e@kernel.org> <20260720-kfree_rcu_nolock-v4-2-964e03c41a4e@kernel.org> From: "Vlastimil Babka (SUSE)" Autocrypt: addr=vbabka@kernel.org; keydata= xsFNBFZdmxYBEADsw/SiUSjB0dM+vSh95UkgcHjzEVBlby/Fg+g42O7LAEkCYXi/vvq31JTB KxRWDHX0R2tgpFDXHnzZcQywawu8eSq0LxzxFNYMvtB7sV1pxYwej2qx9B75qW2plBs+7+YB 87tMFA+u+L4Z5xAzIimfLD5EKC56kJ1CsXlM8S/LHcmdD9Ctkn3trYDNnat0eoAcfPIP2OZ+ 9oe9IF/R28zmh0ifLXyJQQz5ofdj4bPf8ecEW0rhcqHfTD8k4yK0xxt3xW+6Exqp9n9bydiy tcSAw/TahjW6yrA+6JhSBv1v2tIm+itQc073zjSX8OFL51qQVzRFr7H2UQG33lw2QrvHRXqD Ot7ViKam7v0Ho9wEWiQOOZlHItOOXFphWb2yq3nzrKe45oWoSgkxKb97MVsQ+q2SYjJRBBH4 8qKhphADYxkIP6yut/eaj9ImvRUZZRi0DTc8xfnvHGTjKbJzC2xpFcY0DQbZzuwsIZ8OPJCc LM4S7mT25NE5kUTG/TKQCk922vRdGVMoLA7dIQrgXnRXtyT61sg8PG4wcfOnuWf8577aXP1x 6mzw3/jh3F+oSBHb/GcLC7mvWreJifUL2gEdssGfXhGWBo6zLS3qhgtwjay0Jl+kza1lo+Cv BB2T79D4WGdDuVa4eOrQ02TxqGN7G0Biz5ZLRSFzQSQwLn8fbwARAQABzSNWbGFzdGltaWwg QmFia2EgPHZiYWJrYUBrZXJuZWwub3JnPsLBsAQTAQoAWhYhBKlA1DSZLC6OmRA9UCJPp+fM gqZkBQJqFFy6GxSAAAAAAAQADm1hbnUyLDIuNSsxLjEyLDIsMgIbAwUJGtCBUAULCQgHAwUV CgkICwUWAgMBAAIeBQIXgAAKCRAiT6fnzIKmZJIUEADFx/tREzUImHrEwVHeSvDFmA7tJysI UVrlvrM09E7GIuzphzv7jYmo8n3ANpCczLEVr4G0syYQdTigaZgv3+FQDIIzhKih1IHhu1Ei XHlywNWKnQxxQEUNi5Mwx43wQz5XVw9F1A7gtKBKNtfogO511hAbrzagrYajyQacEJ/+sfhZ 9Da8ltHIXD8pcYaHUfQgEusCgmEd9+KrUwrTbckFKmYq5chuE6yJ4J0EmWknL096jIE6CnzF FRslQ3B1UKDjxVsm1ZHfir5NeWszLkTvGFsddFaWTgh8UycESG6VQzKXjjewXu2pG7YQYRpj QKm1W5X2TkwWkXRBZTmfmbhxIUMh3+zf5wQ463rSmDN/8v81tdqBtAW6rH/kzg1GvkaTHXn0 507yEHFzBksk2viAuIxxr7km8+/KARYLIdGtx30EG8cKzAUZOK6WqxtNCsXUJNrVE8CWrCaD icoNu7Fs1c5hmPHdSTnU48ce67449DdnO4neLSNhRiGlMHJgfJUmgrxu/hcYeOZ3haWmEQ2w uW1Mh01OHi8QZHCEyAbABrPs9GUgccc/4eYXX9hIgxfSkYzn8f+8NuIFPWl/0uTvjgqU29FQ SbzOLxHq9439Ox40G5mS5eZXRGxITYR+6TXvRGI6P/264jvflnr/pDGUttaikU+0W+1uxgKH cmYbEc7ATQRbGTU1AQgAn0H6UrFiWcovkh6EXVcl+SeqyO6JHOPm+e9Wu0Vw+VIUvXZVUVVQ La1PQDUi6j00ChlcR66g9/V0sPIcSutacPKfdKYOBvzd4rlhL8rfrdEsQw5ApZxrA8kYZVMh FmBRKAa6wos25moTlMKpCWzTH84+WO5+ziCTsTUZASAToz3RdunTD+vQcHj0GqNTPAHK63sf bAB2I0BslZkXkY1RLb/YhuA6E7JyEd2pilZOrIuBGl/5q2qSakgnAVFWFBR/DO27JuAksYnq +aH8vI0xGvwn75KqSk4UzAkDzWSmO4ZHuahKtQgZNsMYV+PGayRBX9b9zbldzopoLBdqHc4n jQARAQABwsF8BBgBCgAmAhsMFiEEqUDUNJksLo6ZED1QIk+n58yCpmQFAmfIHFQFCRYU6J8A CgkQIk+n58yCpmS2PA//bqN1LfcotmArgElsa+0EGZSQlYgK48pm8WAeTXTngudP9IJ4SuKY HR5RNjHcBeqN+Me0zxRqYzRb8nGanHEkDyf4Im8DQM8d6vbyU+FcPmG4skud4kgS1zMHnlVd SXfSIwKC/hKgdHG8aBV7545Lz9X6Iohea+94wneD0aw/hqF+QWewGZhWJriWAZtvEkzNjQOi 4U9F/trLten/x7bpphDSnDMKJtITbtzATT1Dq7o7VpIUK1nCTQALMuMjKCdi8OdU/+V+R3O4 0PXWvX8qrvqYapVbZ+9KqT74FsuB0Ya9uXwgBF2Q6cRuETZk5vqaqKxzqoQZCO8AOz/58j6O 2RHNy/mZEN+7tJ5Tsq42zVJ4jxsT8b9YplavCMsnBgDeRWhcbYhCyttoL7nYISyWg4kQYZ/P wIV3OuNv2f8iKYsxNsRuClOAF82+gvqOy1/1pprFjy8uo2pkoOrb63aOP3vO5VHnRKgra6dq NcaZ+c6J4H+nEJGi2SkHAUJz5oBzuThvPudLvPA/SK8sKoM01IRxSihev/S/5WLazXB1PGem OCbvzC1IjWJJraxiDJ5IygokapUa2RP7+WBR22skQ3SSl6G107QgWKSyTOGWEaRmV53vxQLV jXuCmzSSasTL60zq5yGrT4/DYQVSNEUiUbG4pYekxJujNeEDkUlky0Y= In-Reply-To: <20260720-kfree_rcu_nolock-v4-2-964e03c41a4e@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 7/20/26 14:44, Harry Yoo (Oracle) wrote: > Teach kfree_rcu_sheaf() how to handle the !allow_spin case. Try to get > an empty sheaf from pcs->spare or the barn even when spinning is not > allowed. Unlike __pcs_replace_full_main(), try harder to allocate > an empty sheaf because the fallback path will be more expensive than > kfree_nolock(). > > Now that slab has internal alloc_flags to describe context, introduce > free_flags analogously and convert free_flags to alloc_flags when > allocating memory in the free path. alloc_empty_sheaf() now strips > __GFP_RECLAIM when SLAB_ALLOC_NOLOCK is specified. > > When trylock fails or the kernel observes non-NULL pcs->rcu_free after > lock acquisition, free the sheaf instead of putting it to the barn. > This is rare and not worth complicating the code. > > Since call_rcu() cannot be called in an unknown context, > kfree_rcu_sheaf() fails when the rcu sheaf becomes full. > > Link: https://lore.kernel.org/linux-mm/872bd673-3d45-4111-8a41-31185db3ece5@kernel.org > Signed-off-by: Harry Yoo (Oracle) LGTM. Reviewed-by: Vlastimil Babka (SUSE) Nits below: > --- > mm/slab.h | 18 +++++++++++++++++- > mm/slab_common.c | 2 +- > mm/slub.c | 36 ++++++++++++++++++++++++++++-------- > 3 files changed, 46 insertions(+), 10 deletions(-) > > diff --git a/mm/slab.h b/mm/slab.h > index 281a65233795..85ef2ebc9812 100644 > --- a/mm/slab.h > +++ b/mm/slab.h > @@ -23,11 +23,27 @@ > #define SLAB_ALLOC_NEW_SLAB 0x02 /* a flag for alloc_slab_obj_exts() */ > #define SLAB_ALLOC_NO_RECURSE 0x04 /* prevent kmalloc() recursion */ > > +#define SLAB_FREE_DEFAULT 0x00 /* no flags */ > +#define SLAB_FREE_NOLOCK 0x01 /* spinning not allowed */ > + > +static inline unsigned int to_alloc_flags(unsigned int free_flags) > +{ > + if (free_flags & SLAB_FREE_NOLOCK) > + return SLAB_ALLOC_NOLOCK; > + else > + return SLAB_ALLOC_DEFAULT; > +} > + > static inline bool alloc_flags_allow_spinning(const unsigned int alloc_flags) > { > return !(alloc_flags & SLAB_ALLOC_NOLOCK); > } > > +static inline bool free_flags_allow_spinning(const unsigned int free_flags) > +{ > + return !(free_flags & SLAB_FREE_NOLOCK); > +} > + > void *__kmalloc_flags_noprof(DECL_TOKEN_PARAMS(size, token), gfp_t flags, > unsigned int alloc_flags, int node) > __assume_kmalloc_alignment __alloc_size(1); > @@ -429,7 +445,7 @@ static inline bool is_kmalloc_normal(struct kmem_cache *s) > return !(s->flags & (SLAB_CACHE_DMA|SLAB_ACCOUNT|SLAB_RECLAIM_ACCOUNT)); > } > > -bool __kfree_rcu_sheaf(struct kmem_cache *s, void *obj); > +bool __kfree_rcu_sheaf(struct kmem_cache *s, void *obj, unsigned int free_flags); > void flush_all_rcu_sheaves(void); > void flush_rcu_sheaves_on_cache(struct kmem_cache *s); > > diff --git a/mm/slab_common.c b/mm/slab_common.c > index b6426d7ceec9..e07b4e6d6679 100644 > --- a/mm/slab_common.c > +++ b/mm/slab_common.c > @@ -1605,7 +1605,7 @@ static bool kfree_rcu_sheaf(void *obj) > > s = slab->slab_cache; > if (likely(!IS_ENABLED(CONFIG_NUMA) || slab_nid(slab) == numa_mem_id())) > - return __kfree_rcu_sheaf(s, obj); > + return __kfree_rcu_sheaf(s, obj, SLAB_FREE_DEFAULT); > > return false; > } > diff --git a/mm/slub.c b/mm/slub.c > index e32a68677537..0c350274fbff 100644 > --- a/mm/slub.c > +++ b/mm/slub.c > @@ -2814,10 +2814,14 @@ static inline struct slab_sheaf *alloc_empty_sheaf(struct kmem_cache *s, > > gfp &= ~OBJCGS_CLEAR_MASK; > > + if (alloc_flags & SLAB_ALLOC_NOLOCK) > + gfp &= ~__GFP_RECLAIM; So in general we expect gfp and alloc flags to be compatible and warn if they are not. This now performs an auto-adjustment, which makes it unusual. But AFAICS only one caller relies on it - __kfree_rcu_sheaf(). So maybe we could just do it there? > + > return __alloc_empty_sheaf(s, gfp, alloc_flags, s->sheaf_capacity); > } > > -static void free_empty_sheaf(struct kmem_cache *s, struct slab_sheaf *sheaf) > +static void __free_empty_sheaf(struct kmem_cache *s, struct slab_sheaf *sheaf, > + bool allow_spin) Why not free_flags instead of allow_spin? Since you already introduced them. > { > /* > * If the sheaf was created with SLAB_ALLOC_NO_RECURSE flag then its > @@ -2829,11 +2833,20 @@ static void free_empty_sheaf(struct kmem_cache *s, struct slab_sheaf *sheaf) > mark_obj_codetag_empty(sheaf); > > VM_WARN_ON_ONCE(sheaf->size > 0); > - kfree(sheaf); > + > + if (likely(allow_spin)) > + kfree(sheaf); > + else > + kfree_nolock(sheaf); > > stat(s, SHEAF_FREE); > } > > +static void free_empty_sheaf(struct kmem_cache *s, struct slab_sheaf *sheaf) > +{ > + __free_empty_sheaf(s, sheaf, /* allow_spin = */ true); Would avoid this ugliness. > +} > + > static unsigned int > refill_objects(struct kmem_cache *s, void **p, gfp_t gfp, unsigned int min, > unsigned int max);