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NetBSD/sys/fs/tmpfs/tmpfs_pool.c

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/* $NetBSD: tmpfs_pool.c,v 1.14 2008/04/28 20:24:02 martin Exp $ */
/*
* Copyright (c) 2005, 2006, 2007 The NetBSD Foundation, Inc.
* All rights reserved.
*
* This code is derived from software contributed to The NetBSD Foundation
* by Julio M. Merino Vidal, developed as part of Google's Summer of Code
* 2005 program.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
* ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
* TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
* BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*/
/*
* Pool allocator and convenience routines for tmpfs.
*/
#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: tmpfs_pool.c,v 1.14 2008/04/28 20:24:02 martin Exp $");
#include <sys/param.h>
#include <sys/pool.h>
#include <sys/atomic.h>
#include <uvm/uvm.h>
#include <fs/tmpfs/tmpfs.h>
/* --------------------------------------------------------------------- */
void * tmpfs_pool_page_alloc(struct pool *, int);
void tmpfs_pool_page_free(struct pool *, void *);
/* XXX: Will go away when our pool allocator does what it has to do by
* itself. */
extern void* pool_page_alloc_nointr(struct pool *, int);
extern void pool_page_free_nointr(struct pool *, void *);
/* --------------------------------------------------------------------- */
/*
* tmpfs provides a custom pool allocator mostly to exactly keep track of
* how many memory is used for each file system instance. These pools are
* never shared across multiple mount points for the reasons described
* below:
*
* - It is very easy to control how many memory is associated with a
* given file system. tmpfs provides a custom pool allocator that
* controls memory usage according to previously specified usage
* limits, by simply increasing or decreasing a counter when pages
* are allocated or released, respectively.
*
* If the pools were shared, we could easily end up with unaccounted
* memory, thus taking incorrect decisions on the amount of memory
* use. As an example to prove this point, consider two mounted
* instances of tmpfs, one mounted on A and another one on B. Assume
* that each memory page can hold up to four directory entries and
* that, for each entry you create on A, you create three on B
* afterwards. After doing this, each memory page will be holding an
* entry from A and three for B. If you sum up all the space taken by
* the total amount of allocated entries, rounded up to a page
* boundary, that number will match the number of allocated pages, so
* everything is fine.
*
* Now suppose we unmount B. Given that the file system has to
* disappear, we have to delete all the directory entries attached to
* it. But the problem is that freeing those entries will not release
* any memory page. Instead, each page will be filled up to a 25%,
* and the rest, a 75%, will be lost. Not lost in a strict term,
* because the memory can be reused by new entries, but lost in the
* sense that it is not accounted by any file system. Despite A will
* think it is using an amount 'X' of memory, it will be really using
* fourth times that number, thus causing mistakes when it comes to
* decide if there is more free space for that specific instance of
* tmpfs.
*
* - The number of page faults and cache misses is reduced given that all
* entries of a given file system are stored in less pages. Note that
* this is true because it is common to allocate and/or access many
* entries at once on a specific file system.
*
* Following the example given above, listing a directory on file system
* A could result, in the worst case scenario, in fourth times more page
* faults if we shared the pools.
*/
struct pool_allocator tmpfs_pool_allocator = {
.pa_alloc = tmpfs_pool_page_alloc,
.pa_free = tmpfs_pool_page_free,
};
/* --------------------------------------------------------------------- */
/*
* Initializes the pool pointed to by tpp and associates it to the mount
* point tmp. The size of its elements is set to size. Its wait channel
* is derived from the string given in what and the mount point given in
* 'tmp', which should result in a unique string among all existing pools.
*/
void
tmpfs_pool_init(struct tmpfs_pool *tpp, size_t size, const char *what,
struct tmpfs_mount *tmp)
{
int cnt;
cnt = snprintf(tpp->tp_name, sizeof(tpp->tp_name),
"%s_tmpfs_%p", what, tmp);
KASSERT(cnt < sizeof(tpp->tp_name));
pool_init(&tpp->tp_pool, size, 0, 0, 0, tpp->tp_name,
&tmpfs_pool_allocator, IPL_NONE);
tpp->tp_mount = tmp;
}
/* --------------------------------------------------------------------- */
/*
* Destroys the pool pointed to by 'tpp'.
*/
void
tmpfs_pool_destroy(struct tmpfs_pool *tpp)
{
pool_destroy((struct pool *)tpp);
}
/* --------------------------------------------------------------------- */
void *
tmpfs_pool_page_alloc(struct pool *pp, int flags)
{
struct tmpfs_pool *tpp;
struct tmpfs_mount *tmp;
unsigned int pages;
void *page;
tpp = (struct tmpfs_pool *)pp;
tmp = tpp->tp_mount;
pages = atomic_inc_uint_nv(&tmp->tm_pages_used);
if (pages >= TMPFS_PAGES_MAX(tmp)) {
atomic_dec_uint(&tmp->tm_pages_used);
return NULL;
}
/*
* tmpfs never specifies PR_WAITOK as we enforce local limits
* on memory allocation. However, we should wait for memory
* to become available if under our limit. XXX The result of
* the TMPFS_PAGES_MAX() check is stale.
*/
page = pool_page_alloc_nointr(pp, flags | PR_WAITOK);
if (page == NULL) {
atomic_dec_uint(&tmp->tm_pages_used);
}
return page;
}
/* --------------------------------------------------------------------- */
void
tmpfs_pool_page_free(struct pool *pp, void *v)
{
struct tmpfs_pool *tpp;
struct tmpfs_mount *tmp;
tpp = (struct tmpfs_pool *)pp;
tmp = tpp->tp_mount;
atomic_dec_uint(&tmp->tm_pages_used);
pool_page_free_nointr(pp, v);
}
/* --------------------------------------------------------------------- */
/*
* Initialize the string pool pointed to by 'tsp' and attach it to the
* 'tmp' mount point.
*/
void
tmpfs_str_pool_init(struct tmpfs_str_pool *tsp, struct tmpfs_mount *tmp)
{
tmpfs_pool_init(&tsp->tsp_pool_16, 16, "str", tmp);
tmpfs_pool_init(&tsp->tsp_pool_32, 32, "str", tmp);
tmpfs_pool_init(&tsp->tsp_pool_64, 64, "str", tmp);
tmpfs_pool_init(&tsp->tsp_pool_128, 128, "str", tmp);
tmpfs_pool_init(&tsp->tsp_pool_256, 256, "str", tmp);
tmpfs_pool_init(&tsp->tsp_pool_512, 512, "str", tmp);
tmpfs_pool_init(&tsp->tsp_pool_1024, 1024, "str", tmp);
}
/* --------------------------------------------------------------------- */
/*
* Destroy the given string pool.
*/
void
tmpfs_str_pool_destroy(struct tmpfs_str_pool *tsp)
{
tmpfs_pool_destroy(&tsp->tsp_pool_16);
tmpfs_pool_destroy(&tsp->tsp_pool_32);
tmpfs_pool_destroy(&tsp->tsp_pool_64);
tmpfs_pool_destroy(&tsp->tsp_pool_128);
tmpfs_pool_destroy(&tsp->tsp_pool_256);
tmpfs_pool_destroy(&tsp->tsp_pool_512);
tmpfs_pool_destroy(&tsp->tsp_pool_1024);
}
/* --------------------------------------------------------------------- */
/*
* Allocate a new string with a minimum length of len from the 'tsp'
* string pool. The pool can return a bigger string, but the caller must
* not make any assumptions about the real object size.
*/
char *
tmpfs_str_pool_get(struct tmpfs_str_pool *tsp, size_t len, int flags)
{
struct tmpfs_pool *p;
KASSERT(len <= 1024);
if (len <= 16) p = &tsp->tsp_pool_16;
else if (len <= 32) p = &tsp->tsp_pool_32;
else if (len <= 64) p = &tsp->tsp_pool_64;
else if (len <= 128) p = &tsp->tsp_pool_128;
else if (len <= 256) p = &tsp->tsp_pool_256;
else if (len <= 512) p = &tsp->tsp_pool_512;
else if (len <= 1024) p = &tsp->tsp_pool_1024;
else {
KASSERT(0);
p = NULL; /* Silence compiler warnings */
}
return (char *)TMPFS_POOL_GET(p, flags);
}
/* --------------------------------------------------------------------- */
/*
* Destroy the str string, which was allocated from the 'tsp' string pool
* with a length of 'len'. The length must match the one given during
* allocation.
*/
void
tmpfs_str_pool_put(struct tmpfs_str_pool *tsp, char *str, size_t len)
{
struct tmpfs_pool *p;
KASSERT(len <= 1024);
if (len <= 16) p = &tsp->tsp_pool_16;
else if (len <= 32) p = &tsp->tsp_pool_32;
else if (len <= 64) p = &tsp->tsp_pool_64;
else if (len <= 128) p = &tsp->tsp_pool_128;
else if (len <= 256) p = &tsp->tsp_pool_256;
else if (len <= 512) p = &tsp->tsp_pool_512;
else if (len <= 1024) p = &tsp->tsp_pool_1024;
else {
KASSERT(0);
p = NULL; /* Silence compiler warnings */
}
TMPFS_POOL_PUT(p, str);
}
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