Messages in this thread | | | From | Johannes Weiner <> | Subject | Re: [PATCH] [6/13] Core maskable allocator | Date | Fri, 07 Mar 2008 11:53:30 +0100 |
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Hi Andi,
Andi Kleen <andi@firstfloor.org> writes:
> Index: linux/mm/mask-alloc.c > =================================================================== > --- /dev/null > +++ linux/mm/mask-alloc.c > @@ -0,0 +1,504 @@ > +/* > + * Generic management of low memory zone to allocate memory with a address mask. > + * > + * The maskable pool is reserved inside another zone, but managed by a > + * specialized bitmap allocator. The allocator is not O(1) (searches > + * the bitmap with a last use hint) but should be fast enough for > + * normal purposes. The advantage of the allocator is that it can > + * allocate based on a mask. > + * > + * The allocator could be improved, but it's better to keep > + * things simple for now and there are relatively few users > + * which are usually not that speed critical. Also for simple > + * repetive allocation patterns it should be approximately usually > + * O(1) anyways due to the rotating cursor in the bitmap. > + * > + * This allocator should be only used by architectures with reasonably > + * continuous physical memory at least for the low normal zone. > + * > + * Note book: > + * Right now there are no high priority reservations (__GFP_HIGH). Iff > + * they are needed it would be possible to reserve some very low memory > + * for those. > + * > + * Copyright 2007, 2008 Andi Kleen, SUSE Labs. > + * Subject to the GNU Public License v.2 only. > + */ > + > +#include <linux/mm.h> > +#include <linux/gfp.h> > +#include <linux/kernel.h> > +#include <linux/sched.h> > +#include <linux/bitops.h> > +#include <linux/string.h> > +#include <linux/wait.h> > +#include <linux/bootmem.h> > +#include <linux/module.h> > +#include <linux/fault-inject.h> > +#include <linux/ctype.h> > +#include <linux/kallsyms.h> > +#include "internal.h" > + > +#define BITS_PER_PAGE (PAGE_SIZE * 8) > + > +#define MASK_ZONE_LIMIT (2U<<30) /* 2GB max for now */ > + > +#define Mprintk(x...) > +#define Mprint_symbol(x...) > + > +static int force_mask __read_mostly; > +static DECLARE_WAIT_QUEUE_HEAD(mask_zone_wait); > +unsigned long mask_timeout __read_mostly = 5*HZ; > + > +/* > + * The mask_bitmap maintains all the pages in the mask pool. > + * It is reversed (lowest pfn has the highest index) > + * to make reverse search easier. > + * All accesses are protected by the mask_bitmap_lock > + */ > +static DEFINE_SPINLOCK(mask_bitmap_lock); > +static unsigned long *mask_bitmap; > +static unsigned long mask_max_pfn; > + > +static inline unsigned pfn_to_maskbm_index(unsigned long pfn) > +{ > + return mask_max_pfn - pfn; > +} > + > +static inline unsigned maskbm_index_to_pfn(unsigned index) > +{ > + return mask_max_pfn - index; > +} > + > +static unsigned wait_for_mask_free(unsigned left) > +{ > + DEFINE_WAIT(wait); > + prepare_to_wait(&mask_zone_wait, &wait, TASK_UNINTERRUPTIBLE); > + left = schedule_timeout(left); > + finish_wait(&mask_zone_wait, &wait); > + return left; > +} > +
If ...
> +/* First try normal zones if possible. */ > +static struct page * > +alloc_higher_pages(gfp_t gfp_mask, unsigned order, unsigned long pfn) > +{ > + struct page *p = NULL; > + if (pfn > mask_max_pfn) { > +#ifdef CONFIG_ZONE_DMA32 > + if (pfn <= (0xffffffff >> PAGE_SHIFT)) { > + p = alloc_pages(gfp_mask|GFP_DMA32|__GFP_NOWARN, > + order);
... this succeeds and allocated pages, and ...
> + if (p && page_to_pfn(p) >= pfn) { > + __free_pages(p, order); > + p = NULL; > + }
... p is and it's pfn is lower than pfn ...
> + } > +#endif > + p = alloc_pages(gfp_mask|__GFP_NOWARN, order);
... isn't this a leak here?
> + if (p && page_to_pfn(p) >= pfn) { > + __free_pages(p, order); > + p = NULL; > + } > + } > + return p; > +} > + > +static unsigned long alloc_mask(int pages, unsigned long max) > +{ > + static unsigned long next_bit; > + unsigned long offset, flags, start, pfn; > + int k; > + > + if (max >= mask_max_pfn) > + max = mask_max_pfn;
Can omit the assignment when max == mask_max_pfn.
> + start = mask_max_pfn - max; > + > + spin_lock_irqsave(&mask_bitmap_lock, flags); > + offset = -1L; > + > + if (next_bit >= start && next_bit + pages < (mask_max_pfn - (max>>1))) { > + offset = find_next_zero_string(mask_bitmap, next_bit, > + mask_max_pfn, pages); > + if (offset != -1L) > + count_vm_events(MASK_BITMAP_SKIP, offset - next_bit); > + } > + if (offset == -1L) { > + offset = find_next_zero_string(mask_bitmap, start, > + mask_max_pfn, pages); > + if (offset != -1L) > + count_vm_events(MASK_BITMAP_SKIP, offset - start); > + } > + if (offset != -1L) { > + for (k = 0; k < pages; k++) { > + BUG_ON(test_bit(offset + k, mask_bitmap)); > + set_bit(offset + k, mask_bitmap); > + } > + next_bit = offset + pages; > + if (next_bit >= mask_max_pfn) > + next_bit = start; > + } > + spin_unlock_irqrestore(&mask_bitmap_lock, flags); > + if (offset == -1L) > + return -1L; > + > + offset += pages - 1; > + pfn = maskbm_index_to_pfn(offset); > + > + BUG_ON(maskbm_index_to_pfn(offset) != pfn); > + return pfn; > +}
Hannes
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