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 63B401C2432 for ; Mon, 10 Feb 2025 14:01:43 +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=1739196104; cv=none; b=GNOOaWe4ROWo3K8GXPda/Y9Fy0QaXD4wOXnOJESIJnuCi56VjXRqhSGDy0qHiwPLg1ZL0+45J98Arnef3xpSzOK0pzdtGdVDNpyWULEILPXm8kVr0ZKnuakWeX/vvl6xTkQk0NeWFLdoBKjYVc5Ovw13Fh810XiUGtsJ+blMT1s= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1739196104; c=relaxed/simple; bh=jZ45VJM1FkUFWBWnJA/W8+INLQ9eu+cYDQWx5ccXMhg=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=MWuqpCKC7byPjOAOunnzou5jpVgYnWxHzEX6lD2YXNEmZDdkJmusOeyssnHa43y5jEFComU9tPCYUQXaHRvdlkY+E0pZPx7+9/l7j01vABfDKdM5ljEhkbn62Mr3AVlGGmpAqECIL22aUFBbI5hw/HXBj/rpD06/gAuNMidYu7I= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Ga3F4OYc; 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="Ga3F4OYc" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1C189C4CED1; Mon, 10 Feb 2025 14:01:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1739196103; bh=jZ45VJM1FkUFWBWnJA/W8+INLQ9eu+cYDQWx5ccXMhg=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=Ga3F4OYc2I27f5PzW7R7wwie0uwzxbWlS48Ba++HWl+UzLhN461lbPYMEPXe9LDSc 50pJQRETf6aNUXZTTaytJVg5M35jFC2xt8TfPHfYUC4624eJoRNm3E2+DrpL7Gf6Iv +uSqF7n/IfqPZE7ehSt0nVvV+t8tdoN2RDQSBK/OcGZVTKxEwQCrgwNvDlObVOCroa FGmSF7nz5224GGEEyQWCM0GSnpJrueH6iqzxs7m0xjkFAp/+NZPWuCM9V2hjcqII3S rgqUAadFJAzKXdaLK6Q9LoVqW+E4+T+fYpE7t/hXz2sUc7cKCk58AAxNnZrrCHtlOx layKlYE7PRqmQ== Message-ID: <5e6060d79e247a7e97443f200399061da8d558f9.camel@kernel.org> Subject: Re: [PATCH 4/6] nfsd: filecache: introduce NFSD_FILE_RECENT From: Jeff Layton To: NeilBrown , Chuck Lever Cc: linux-nfs@vger.kernel.org, Olga Kornievskaia , Dai Ngo , Tom Talpey , Dave Chinner Date: Mon, 10 Feb 2025 09:01:41 -0500 In-Reply-To: <20250207051701.3467505-5-neilb@suse.de> References: <20250207051701.3467505-1-neilb@suse.de> <20250207051701.3467505-5-neilb@suse.de> Autocrypt: addr=jlayton@kernel.org; prefer-encrypt=mutual; keydata=mQINBE6V0TwBEADXhJg7s8wFDwBMEvn0qyhAnzFLTOCHooMZyx7XO7dAiIhDSi7G1NPxw n8jdFUQMCR/GlpozMFlSFiZXiObE7sef9rTtM68ukUyZM4pJ9l0KjQNgDJ6Fr342Htkjxu/kFV1Wv egyjnSsFt7EGoDjdKqr1TS9syJYFjagYtvWk/UfHlW09X+jOh4vYtfX7iYSx/NfqV3W1D7EDi0PqV T2h6v8i8YqsATFPwO4nuiTmL6I40ZofxVd+9wdRI4Db8yUNA4ZSP2nqLcLtFjClYRBoJvRWvsv4lm 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2tAMJUvFTdDbfe3zKlPDTuVsyNsALBGclPLagJ5ZTP+Vp2irAN9uwBuacBOTtmOdz4ZN2tdvNgozz uxp4CHBDVzAslUi2idy+xpsp47DWPxYFIRP3M8QG/aNW052LaPc0cedYxp8+9eiVUNpxF4SiU4i9J DfX/sn9XcfoVZIxMpCRE750zvJvcCUz9HojsrMQ1NFc7MFT1z3MOW2/RlzPcog7xvR5ENPH19ojRD CHqumUHRry+RF0lH00clzX/W8OrQJZtoBPXv9ahka/Vp7kEulcBJr1cH5Wz/WprhsIM7U9pse1f1g Yy9YbXtWctUz8uvDR7shsQxAhX3qO7DilMtuGo1v97I/Kx4gXQ52syh/w6EBny71CZrOgD6kJwPVV AaM1LRC28muq91WCFhs/nzHozpbzcheyGtMUI2Ao4K6mnY+3zIuXPygZMFr9KXE6fF7HzKxKuZMJO aEZCiDOq0anx6FmOzs5E6Jqdpo/mtI8beK+BE7Va6ni7YrQlnT0i3vaTVMTiCThbqsB20VrbMjlhp f8lfK1XVNbRq/R7GZ9zHESlsa35ha60yd/j3pu5hT2xyy8krV8vGhHvnJ1XRMJBAB/UYb6FyC7S+m QZIQXVeAA+smfTT0tDrisj1U5x6ZB9b3nBg65kc= Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.54.3 (3.54.3-1.fc41) Precedence: bulk X-Mailing-List: linux-nfs@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Fri, 2025-02-07 at 16:15 +1100, NeilBrown wrote: > The filecache lru is walked in 2 circumstances for 2 different reasons. >=20 > 1/ When called from the shrinker we want to discard the first few > entries on the list, ignoring any with NFSD_FILE_REFERENCED set > because they should really be at the end of the LRU as they have been > referenced recently. So those ones are ROTATED. >=20 > 2/ When called from the nfsd_file_gc() timer function we want to discard > anything that hasn't been used since before the previous call, and > mark everything else as unused at this point in time. >=20 > Using the same flag for both of these can result in some unexpected > outcomes. If the shrinker callback clears NFSD_FILE_REFERENCED then the > nfsd_file_gc() will think the file hasn't been used in a while, while > really it has. >=20 > I think it is easier to reason about the behaviour if we instead have > two flags. >=20 > NFSD_FILE_REFERENCED means "this should be at the end of the LRU, please > put it there when convenient" > NFSD_FILE_RECENT means "this has been used recently - since the last > run of nfsd_file_gc() >=20 > When either caller finds an NFSD_FILE_REFERENCED entry, that entry > should be moved to the end of the LRU and the flag cleared. This can > safely happen at any time. The actual order on the lru might not be > strictly least-recently-used, but that is normal for linux lrus. >=20 > The shrinker callback can ignore the "recent" flag. If it ends up > freeing something that is "recent" that simply means that memory > pressure is sufficient to limit the acceptable cache age to less than > the nfsd_file_gc frequency. >=20 > The gc caller should primarily focus on NFSD_FILE_RECENT. It should > free everything that doesn't have this flag set, and should clear the > flag on everything else. When it clears the flag it is convenient to > clear the "REFERENCED" flag and move to the end of the LRU too. >=20 > With this, calls from the shrinker do not prematurely age files. It > will focus only on freeing those that are least recently used. >=20 > Signed-off-by: NeilBrown > --- > fs/nfsd/filecache.c | 21 +++++++++++++++++++-- > fs/nfsd/filecache.h | 1 + > fs/nfsd/trace.h | 3 +++ > 3 files changed, 23 insertions(+), 2 deletions(-) >=20 > diff --git a/fs/nfsd/filecache.c b/fs/nfsd/filecache.c > index 04588c03bdfe..9faf469354a5 100644 > --- a/fs/nfsd/filecache.c > +++ b/fs/nfsd/filecache.c > @@ -318,10 +318,10 @@ nfsd_file_check_writeback(struct nfsd_file *nf) > mapping_tagged(mapping, PAGECACHE_TAG_WRITEBACK); > } > =20 > - > static bool nfsd_file_lru_add(struct nfsd_file *nf) > { > set_bit(NFSD_FILE_REFERENCED, &nf->nf_flags); > + set_bit(NFSD_FILE_RECENT, &nf->nf_flags); Technically, I don't think you need the REFERENCED bit at all. This is the only place it's set, and below this is calling list_lru_add_obj(). That returns false if the object was already on a per-node LRU. Instead of that, you could add a list_lru helper that will rotate the object to the end of its nodelist if it's already on one. OTOH, that might mean more cross NUMA-node accesses to the spinlocks than we get by using a flag and doing this at GC time. > if (list_lru_add_obj(&nfsd_file_lru, &nf->nf_lru)) { > trace_nfsd_file_lru_add(nf); > return true; > @@ -528,6 +528,23 @@ nfsd_file_lru_cb(struct list_head *item, struct list= _lru_one *lru, > return LRU_REMOVED; > } > =20 > +static enum lru_status > +nfsd_file_gc_cb(struct list_head *item, struct list_lru_one *lru, > + void *arg) > +{ > + struct nfsd_file *nf =3D list_entry(item, struct nfsd_file, nf_lru); > + > + if (test_and_clear_bit(NFSD_FILE_RECENT, &nf->nf_flags)) { > + /* "REFERENCED" really means "should be at the end of the LRU. > + * As we are putting it there we can clear the flag > + */ > + clear_bit(NFSD_FILE_REFERENCED, &nf->nf_flags); > + trace_nfsd_file_gc_aged(nf); > + return LRU_ROTATE; > + } > + return nfsd_file_lru_cb(item, lru, arg); > +} > + > static void > nfsd_file_gc(void) > { > @@ -537,7 +554,7 @@ nfsd_file_gc(void) > =20 > for_each_node_state(nid, N_NORMAL_MEMORY) { > unsigned long nr =3D list_lru_count_node(&nfsd_file_lru, nid); > - ret +=3D list_lru_walk_node(&nfsd_file_lru, nid, nfsd_file_lru_cb, > + ret +=3D list_lru_walk_node(&nfsd_file_lru, nid, nfsd_file_gc_cb, > &dispose, &nr); > } > trace_nfsd_file_gc_removed(ret, list_lru_count(&nfsd_file_lru)); > diff --git a/fs/nfsd/filecache.h b/fs/nfsd/filecache.h > index d5db6b34ba30..de5b8aa7fcb0 100644 > --- a/fs/nfsd/filecache.h > +++ b/fs/nfsd/filecache.h > @@ -38,6 +38,7 @@ struct nfsd_file { > #define NFSD_FILE_PENDING (1) > #define NFSD_FILE_REFERENCED (2) > #define NFSD_FILE_GC (3) > +#define NFSD_FILE_RECENT (4) > unsigned long nf_flags; > refcount_t nf_ref; > unsigned char nf_may; > diff --git a/fs/nfsd/trace.h b/fs/nfsd/trace.h > index ad2c0c432d08..9af723eeb2b0 100644 > --- a/fs/nfsd/trace.h > +++ b/fs/nfsd/trace.h > @@ -1039,6 +1039,7 @@ DEFINE_CLID_EVENT(confirmed_r); > { 1 << NFSD_FILE_HASHED, "HASHED" }, \ > { 1 << NFSD_FILE_PENDING, "PENDING" }, \ > { 1 << NFSD_FILE_REFERENCED, "REFERENCED" }, \ > + { 1 << NFSD_FILE_RECENT, "RECENT" }, \ > { 1 << NFSD_FILE_GC, "GC" }) > =20 > DECLARE_EVENT_CLASS(nfsd_file_class, > @@ -1317,6 +1318,7 @@ DEFINE_NFSD_FILE_GC_EVENT(nfsd_file_lru_del_dispose= d); > DEFINE_NFSD_FILE_GC_EVENT(nfsd_file_gc_in_use); > DEFINE_NFSD_FILE_GC_EVENT(nfsd_file_gc_writeback); > DEFINE_NFSD_FILE_GC_EVENT(nfsd_file_gc_referenced); > +DEFINE_NFSD_FILE_GC_EVENT(nfsd_file_gc_aged); > DEFINE_NFSD_FILE_GC_EVENT(nfsd_file_gc_disposed); > =20 > DECLARE_EVENT_CLASS(nfsd_file_lruwalk_class, > @@ -1346,6 +1348,7 @@ DEFINE_EVENT(nfsd_file_lruwalk_class, name, \ > TP_ARGS(removed, remaining)) > =20 > DEFINE_NFSD_FILE_LRUWALK_EVENT(nfsd_file_gc_removed); > +DEFINE_NFSD_FILE_LRUWALK_EVENT(nfsd_file_gc_recent); > DEFINE_NFSD_FILE_LRUWALK_EVENT(nfsd_file_shrinker_removed); > =20 > TRACE_EVENT(nfsd_file_close, Reviewed-by: Jeff Layton