From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 4C262286281 for ; Tue, 18 Feb 2025 20:51:46 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1739911907; cv=none; b=QLo+J5BOoeCb7x96SPnkhHI5s5+O9ehPXyFs5jYcwllNaTcxePPVdD66LAjuYJ0XoQn9cZDXFOphok6sGXybQdx59uvYSv9blZuzE95hMfZakczkrueBPCowxFh8FR8GGTqvDPnb0ZDJSJxzHxAFOIStGRcpqLGRGKjbMO+Y464= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1739911907; c=relaxed/simple; bh=cKW3HEFyck4+D3GvB/fCkP5yG02JSXzd06+4bfS+8So=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=VZucpYZlKsVg2PSnRMrcL+3cdLSjo6s5alvKS2yc2JmrO1nd3GuouIJhcv0m61OMpB7/o6PxSC+w1JNrbJltIF/eC/Sjq3S6Vddr8DHnkm38XD8f3R1OLPF02rfTY9CJIw9Gsq0m2d3zbYq7uSkKwHCLTmSwDDZeqnBcVvWGqYs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=ERwJe2tJ; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="ERwJe2tJ" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 22F2CC4CEE2; Tue, 18 Feb 2025 20:51:46 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1739911906; bh=cKW3HEFyck4+D3GvB/fCkP5yG02JSXzd06+4bfS+8So=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=ERwJe2tJwbwm1ltnHX0kxip4BYdBQB47t8wZbcrxzK5/PfsoE92lFNSXkOOSZb7Fs I5j1LecYU1ie+bduAheSoIS9NxNag+1kOD5TbYdT/Jjy7TzSx50NFErBa57ep9pMRK bM6PIc5ty/GlJjHNNsBLRfObPPisnmNBHc+dFn+OSzd/+IZRHlJaeh0DCC1L5a/3Sg Z8LlB6YpEMAVimyTroirk2ZjgH5SXAnqXiFVYQ9ypqGwqu9RQbx61NtRekH71WuKmz xaOVuxohHthd7t8T08YG9hIj5xVrWhwsq0/cAM2vp+oirjbY1WDfGJnKRyLfIJjkkp 8nEmFtQkonYKA== Message-ID: Subject: Re: [PATCH v2 7/7] nfsd: filecache: drop the list_lru lock during lock gc scans From: Jeff Layton To: cel@kernel.org, Neil Brown , Olga Kornievskaia , Dai Ngo , Tom Talpey Cc: linux-nfs@vger.kernel.org, Dave Chinner Date: Tue, 18 Feb 2025 15:51:44 -0500 In-Reply-To: <20250218153937.6125-8-cel@kernel.org> References: <20250218153937.6125-1-cel@kernel.org> <20250218153937.6125-8-cel@kernel.org> Autocrypt: addr=jlayton@kernel.org; prefer-encrypt=mutual; keydata=mQINBE6V0TwBEADXhJg7s8wFDwBMEvn0qyhAnzFLTOCHooMZyx7XO7dAiIhDSi7G1NPxw n8jdFUQMCR/GlpozMFlSFiZXiObE7sef9rTtM68ukUyZM4pJ9l0KjQNgDJ6Fr342Htkjxu/kFV1Wv egyjnSsFt7EGoDjdKqr1TS9syJYFjagYtvWk/UfHlW09X+jOh4vYtfX7iYSx/NfqV3W1D7EDi0PqV T2h6v8i8YqsATFPwO4nuiTmL6I40ZofxVd+9wdRI4Db8yUNA4ZSP2nqLcLtFjClYRBoJvRWvsv4lm 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Under a high NFSv3 load with lots of different files being accessed, > the LRU list of garbage-collectable files can become quite long. >=20 > Asking list_lru_scan_node() to scan the whole list can result in a long > period during which a spinlock is held, blocking the addition of new LRU > items. >=20 > So ask list_lru_scan_node() to scan only a few entries at a time, and > repeat until the scan is complete. >=20 > If the shrinker runs between two consecutive calls of > list_lru_scan_node() it could invalidate the "remaining" counter which > could lead to premature freeing. So add a spinlock to avoid that. >=20 > Signed-off-by: NeilBrown > Signed-off-by: Chuck Lever > --- > fs/nfsd/filecache.c | 27 ++++++++++++++++++++++++--- > fs/nfsd/filecache.h | 6 ++++++ > 2 files changed, 30 insertions(+), 3 deletions(-) >=20 > diff --git a/fs/nfsd/filecache.c b/fs/nfsd/filecache.c > index 56935349f0e4..9a41ccfc2df6 100644 > --- a/fs/nfsd/filecache.c > +++ b/fs/nfsd/filecache.c > @@ -544,6 +544,13 @@ nfsd_file_gc_cb(struct list_head *item, struct list_= lru_one *lru, > return nfsd_file_lru_cb(item, lru, arg); > } > =20 > +/* If the shrinker runs between calls to list_lru_walk_node() in > + * nfsd_file_gc(), the "remaining" count will be wrong. This could > + * result in premature freeing of some files. This may not matter much > + * but is easy to fix with this spinlock which temporarily disables > + * the shrinker. > + */ > +static DEFINE_SPINLOCK(nfsd_gc_lock); Having this as a global lock makes sense since there is just a single shrinker and laundrette for the whole kernel. I don't think it's worthwhile to make them per-net or anything either. =20 > static void > nfsd_file_gc(void) > { > @@ -551,12 +558,22 @@ nfsd_file_gc(void) > LIST_HEAD(dispose); > int nid; > =20 > + spin_lock(&nfsd_gc_lock); > for_each_node_state(nid, N_NORMAL_MEMORY) { > - unsigned long nr =3D list_lru_count_node(&nfsd_file_lru, nid); > + unsigned long remaining =3D list_lru_count_node(&nfsd_file_lru, nid); > =20 > - ret +=3D list_lru_walk_node(&nfsd_file_lru, nid, nfsd_file_gc_cb, > - &dispose, &nr); > + while (remaining > 0) { > + unsigned long nr =3D min(remaining, NFSD_FILE_GC_BATCH); > + > + remaining -=3D nr; > + ret +=3D list_lru_walk_node(&nfsd_file_lru, nid, nfsd_file_gc_cb, > + &dispose, &nr); > + if (nr) > + /* walk aborted early */ > + remaining =3D 0; > + } > } Now that I look, if we end up walking a long list on a different NUMA node, this could mean a lot of cross-node calls. This is probably in the "further work" category, but... Maybe we should switch the laundrette to have a work struct per-node, and then schedule all of them on their respective nodes when we start the laundrette. If you do that, then the nfsd_gc_lock could also be per-node. > + spin_unlock(&nfsd_gc_lock); > trace_nfsd_file_gc_removed(ret, list_lru_count(&nfsd_file_lru)); > nfsd_file_dispose_list_delayed(&dispose); > } > @@ -581,8 +598,12 @@ nfsd_file_lru_scan(struct shrinker *s, struct shrink= _control *sc) > LIST_HEAD(dispose); > unsigned long ret; > =20 > + if (!spin_trylock(&nfsd_gc_lock)) > + return SHRINK_STOP; > + > ret =3D list_lru_shrink_walk(&nfsd_file_lru, sc, > nfsd_file_lru_cb, &dispose); > + spin_unlock(&nfsd_gc_lock); > trace_nfsd_file_shrinker_removed(ret, list_lru_count(&nfsd_file_lru)); > nfsd_file_dispose_list_delayed(&dispose); > return ret; > diff --git a/fs/nfsd/filecache.h b/fs/nfsd/filecache.h > index de5b8aa7fcb0..5865f9c72712 100644 > --- a/fs/nfsd/filecache.h > +++ b/fs/nfsd/filecache.h > @@ -3,6 +3,12 @@ > =20 > #include > =20 > +/* > + * Limit the time that the list_lru_one lock is held during > + * an LRU scan. > + */ > +#define NFSD_FILE_GC_BATCH (16UL) > + > /* > * This is the fsnotify_mark container that nfsd attaches to the files t= hat it > * is holding open. Note that we have a separate refcount here aside fro= m the No objection to this patch as an interim step though. Reviewed-by: Jeff Layton