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c2fa09454e
The port of XFS to Linux introduced a thread-specific PF_FSTRANS bit that is used to mark contexts which are processing transactions. When set, allocations in this context can dip into kernel memory reserves to avoid deadlocks during writeback. Linux 3.9 provided the additional PF_MEMALLOC_NOIO for disabling __GFP_IO in page allocations, which XFS began using in 3.15. This patch implements hooks for marking transactions via PF_FSTRANS. When an allocation is performed in the context of PF_FSTRANS, any KM_SLEEP allocation is transparently converted to a GFP_NOIO allocation. Additionally, when using a Linux 3.9 or newer kernel, it will set PF_MEMALLOC_NOIO to prevent direct reclaim from entering pageout() on on any KM_PUSHPAGE or KM_NOSLEEP allocation. This effectively allows the spl_vmalloc() helper function to be used safely in a thread which is responsible for IO. Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
110 lines
4.4 KiB
C
110 lines
4.4 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_VMEM_H
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#define _SPL_VMEM_H
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#include <sys/kmem.h>
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#include <linux/sched.h>
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#include <linux/vmalloc.h>
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typedef struct vmem { } vmem_t;
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extern vmem_t *heap_arena;
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extern vmem_t *zio_alloc_arena;
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extern vmem_t *zio_arena;
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extern size_t vmem_size(vmem_t *vmp, int typemask);
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extern void *spl_vmalloc(unsigned long size, gfp_t lflags, pgprot_t prot);
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/*
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* Memory allocation interfaces
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*/
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#define VMEM_ALLOC 0x01
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#define VMEM_FREE 0x02
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#ifndef VMALLOC_TOTAL
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#define VMALLOC_TOTAL (VMALLOC_END - VMALLOC_START)
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#endif
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/*
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* vmem_* is an interface to a low level arena-based memory allocator on
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* Illumos that is used to allocate virtual address space. The kmem SLAB
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* allocator allocates slabs from it. Then the generic allocation functions
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* kmem_{alloc,zalloc,free}() are layered on top of SLAB allocators.
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*
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* On Linux, the primary means of doing allocations is via kmalloc(), which
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* is similarly layered on top of something called the buddy allocator. The
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* buddy allocator is not available to kernel modules, it uses physical
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* memory addresses rather than virtual memory addresses and is prone to
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* fragmentation.
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*
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* Linux sets aside a relatively small address space for in-kernel virtual
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* memory from which allocations can be done using vmalloc(). It might seem
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* like a good idea to use vmalloc() to implement something similar to
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* Illumos' allocator. However, this has the following problems:
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*
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* 1. Page directory table allocations are hard coded to use GFP_KERNEL.
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* Consequently, any KM_PUSHPAGE or KM_NOSLEEP allocations done using
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* vmalloc() will not have proper semantics.
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*
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* 2. Address space exhaustion is a real issue on 32-bit platforms where
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* only a few 100MB are available. The kernel will handle it by spinning
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* when it runs out of address space.
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*
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* 3. All vmalloc() allocations and frees are protected by a single global
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* lock which serializes all allocations.
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*
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* 4. Accessing /proc/meminfo and /proc/vmallocinfo will iterate the entire
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* list. The former will sum the allocations while the latter will print
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* them to user space in a way that user space can keep the lock held
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* indefinitely. When the total number of mapped allocations is large
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* (several 100,000) a large amount of time will be spent waiting on locks.
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*
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* 5. Linux has a wait_on_bit() locking primitive that assumes physical
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* memory is used, it simply does not work on virtual memory. Certain
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* Linux structures (e.g. the superblock) use them and might be embedded
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* into a structure from Illumos. This makes using Linux virtual memory
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* unsafe in certain situations.
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*
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* It follows that we cannot obtain identical semantics to those on Illumos.
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* Consequently, we implement the kmem_{alloc,zalloc,free}() functions in
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* such a way that they can be used as drop-in replacements for small vmem_*
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* allocations (8MB in size or smaller) and map vmem_{alloc,zalloc,free}()
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* to them.
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*/
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#define vmem_alloc(sz, fl) spl_vmem_alloc((sz), (fl), __func__, __LINE__)
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#define vmem_zalloc(sz, fl) spl_vmem_zalloc((sz), (fl), __func__, __LINE__)
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#define vmem_free(ptr, sz) spl_vmem_free((ptr), (sz))
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extern void *spl_vmem_alloc(size_t sz, int fl, const char *func, int line);
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extern void *spl_vmem_zalloc(size_t sz, int fl, const char *func, int line);
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extern void spl_vmem_free(const void *ptr, size_t sz);
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int spl_vmem_init(void);
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void spl_vmem_fini(void);
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#endif /* _SPL_VMEM_H */
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