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The SPL provides a wrapper for the kernel's shrinker callbacks, which enables the ZFS code to interface with multiple versions of the shrinker API's from different kernel versions. Specifically, Linux kernels 3.0 - 3.11 has a single "combined" callback, and Linux kernels 3.12 and later have two "split" callbacks. The SPL provides a wrapper function so that the ZFS code only needs to implement one version of the callbacks. Currently the SPL's wrappers are designed such that the ZFS code implements the older, "combined" callback. There are a few downsides to this approach: * The general design within ZFS is for the latest Linux kernel to be considered the "first class" API. * The newer, "split" callback API is easier to understand, because each callback has one purpose. * The current wrappers do not completely abstract out the differing API's, so ZFS code needs `#ifdef` code to handle the differing return values required for different kernel versions. This commit addresses these drawbacks by having the ZFS code provide the latest, "split" callbacks, and the SPL provides a wrapping function for the older, "combined" API. Reviewed-by: Pavel Zakharov <pavel.zakharov@delphix.com> Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov> Signed-off-by: Matthew Ahrens <mahrens@delphix.com> Closes #10502
111 lines
3.4 KiB
C
111 lines
3.4 KiB
C
/*
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* Copyright (C) 2007-2010 Lawrence Livermore National Security, LLC.
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* Copyright (C) 2007 The Regents of the University of California.
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* Produced at Lawrence Livermore National Laboratory (cf, DISCLAIMER).
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* Written by Brian Behlendorf <behlendorf1@llnl.gov>.
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* UCRL-CODE-235197
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*
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* This file is part of the SPL, Solaris Porting Layer.
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* For details, see <http://zfsonlinux.org/>.
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*
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* The SPL is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License as published by the
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* Free Software Foundation; either version 2 of the License, or (at your
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* option) any later version.
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*
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* The SPL is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* for more details.
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*
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* You should have received a copy of the GNU General Public License along
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* with the SPL. If not, see <http://www.gnu.org/licenses/>.
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*/
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#ifndef _SPL_SHRINKER_H
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#define _SPL_SHRINKER_H
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#include <linux/mm.h>
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#include <linux/fs.h>
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/*
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* Due to frequent changes in the shrinker API the following
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* compatibility wrappers should be used. They are as follows:
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*
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* SPL_SHRINKER_DECLARE(varname, countfunc, scanfunc, seek_cost);
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*
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* SPL_SHRINKER_DECLARE is used to declare a shrinker with the name varname,
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* which is passed to spl_register_shrinker()/spl_unregister_shrinker().
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* The countfunc returns the number of free-able objects.
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* The scanfunc returns the number of objects that were freed.
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* The callbacks can return SHRINK_STOP if further calls can't make any more
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* progress. Note that a return value of SHRINK_EMPTY is currently not
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* supported.
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*
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* Example:
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*
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* static unsigned long
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* my_count(struct shrinker *shrink, struct shrink_control *sc)
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* {
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* ...calculate number of objects in the cache...
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*
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* return (number of objects in the cache);
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* }
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*
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* static unsigned long
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* my_scan(struct shrinker *shrink, struct shrink_control *sc)
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* {
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* ...scan objects in the cache and reclaim them...
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* }
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*
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* SPL_SHRINKER_DECLARE(my_shrinker, my_count, my_scan, DEFAULT_SEEKS);
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*
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* void my_init_func(void) {
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* spl_register_shrinker(&my_shrinker);
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* }
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*/
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#define spl_register_shrinker(x) register_shrinker(x)
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#define spl_unregister_shrinker(x) unregister_shrinker(x)
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/*
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* Linux 3.0 to 3.11 Shrinker API Compatibility.
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*/
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#if defined(HAVE_SINGLE_SHRINKER_CALLBACK)
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#define SPL_SHRINKER_DECLARE(varname, countfunc, scanfunc, seek_cost) \
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static int \
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__ ## varname ## _wrapper(struct shrinker *shrink, struct shrink_control *sc)\
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{ \
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if (sc->nr_to_scan != 0) { \
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(void) scanfunc(shrink, sc); \
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} \
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return (countfunc(shrink, sc)); \
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} \
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\
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static struct shrinker varname = { \
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.shrink = __ ## varname ## _wrapper, \
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.seeks = seek_cost \
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}
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#define SHRINK_STOP (-1)
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/*
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* Linux 3.12 and later Shrinker API Compatibility.
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*/
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#elif defined(HAVE_SPLIT_SHRINKER_CALLBACK)
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#define SPL_SHRINKER_DECLARE(varname, countfunc, scanfunc, seek_cost) \
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static struct shrinker varname = { \
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.count_objects = countfunc, \
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.scan_objects = scanfunc, \
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.seeks = seek_cost \
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}
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#else
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/*
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* Linux 2.x to 2.6.22, or a newer shrinker API has been introduced.
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*/
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#error "Unknown shrinker callback"
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#endif
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#endif /* SPL_SHRINKER_H */
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