从free到page cache

// proc_misc.c

static int meminfo_read_proc(char *page, char **start, off_t off,

                                      int count, int *eof, void *data)

{

…

struct sysinfo i;

         si_meminfo(&i); //统计memory的使用情况

         si_swapinfo(&i); //统计swap的使用情况

…

         len = sprintf(page,

                   "MemTotal:     %8lu kB\n"

                   "MemFree:      %8lu kB\n"

                   "Buffers:      %8lu kB\n"

                   "Cached:       %8lu kB\n"

                   "SwapCached:   %8lu kB\n"

…

                   K(i.totalram),

                  K(i.freeram),

                   K(i.bufferram),

                   K(get_page_cache_size()-total_swapcache_pages-i.bufferram),

                   K(total_swapcache_pages),

…

}

struct sysinfo {

         long uptime;                      /* Seconds since boot */

         unsigned long loads[3];          /* 1, 5, and 15 minute load averages */

         unsigned long totalram;                  /*总的页框数,Total usable main memory size */

         unsigned long freeram;                   /* Available memory size */

         unsigned long sharedram;    /* Amount of shared memory */

         unsigned long bufferram;     /* Memory used by buffers */

         unsigned long totalswap;       /* Total swap space size */

         unsigned long freeswap;                 /* swap space still available */

         unsigned short procs;            /* Number of current processes */

         unsigned short pad;                /* explicit padding for m68k */

         unsigned long totalhigh;        /* Total high memory size */

         unsigned long freehigh;                  /* Available high memory size */

         unsigned int mem_unit;                  /* Memory unit size in bytes */

         char _f[20-2*sizeof(long)-sizeof(int)]; /* Padding: libc5 uses this.. */

};

void si_meminfo(struct sysinfo *val)

{

         val->totalram = totalram_pages;//总的页框数

         val->sharedram = 0;

         val->freeram = nr_free_pages();//计算空闲页框数

         val->bufferram = nr_blockdev_pages();//block device使用的面框数

#ifdef CONFIG_HIGHMEM

         val->totalhigh = totalhigh_pages;

         val->freehigh = nr_free_highpages();

#else

         val->totalhigh = 0;

         val->freehigh = 0;

#endif

         val->mem_unit = PAGE_SIZE;

}

//遍历所有的块设备，累加相应的页面数量

long nr_blockdev_pages(void)

{

         struct list_head *p;

         long ret = 0;

         spin_lock(&bdev_lock);

         list_for_each(p, &all_bdevs) {

                   struct block_device *bdev;

                   bdev = list_entry(p, struct block_device, bd_list);

                   ret += bdev->bd_inode->i_mapping->nrpages;

         }

         spin_unlock(&bdev_lock);

         return ret;

}

static inline unsigned long get_page_cache_size(void)

{

         int ret = atomic_read(&nr_pagecache);

         if (unlikely(ret < 0))

                   ret = 0;

         return ret;

}

// include/buffer_head.h

struct buffer_head {

         /* First cache line: */

         unsigned long b_state;            /* buffer state bitmap (see above) */

         struct buffer_head *b_this_page;/* circular list of page's buffers */

         struct page *b_page;               /* the page this bh is mapped to,页框 */

         atomic_t b_count;            /* users using this block */

         u32 b_size;                        /* block size */

         sector_t b_blocknr;                   /* block number,块设备中的逻辑块号 */

         char *b_data;                     /* pointer to data block */

         struct block_device *b_bdev;//块设备

         bh_end_io_t *b_end_io;           /* I/O completion */

        void *b_private;               /* reserved for b_end_io */

         struct list_head b_assoc_buffers; /* associated with another mapping */

};

///对于块设备文件和数据块不相邻的普通文件,都会调用该方法

int block_read_full_page(struct page *page, get_block_t *get_block)

{

…

         if (!page_has_buffers(page))///page没有分配buffer head,见buffer_head.h

                   create_empty_buffers(page, blocksize, 0);//为page创建buffer_head

         head = page_buffers(page);

}

static int

do_no_page(struct mm_struct *mm, struct vm_area_struct *vma,

         unsigned long address, int write_access, pte_t *page_table, pmd_t *pmd)

{

…

          //写私有内存映射,则复制页面

         if (write_access && !(vma->vm_flags & VM_SHARED)) {

                   struct page *page;

                   if (unlikely(anon_vma_prepare(vma)))

                            goto oom;

                   page = alloc_page_vma(GFP_HIGHUSER, vma, address);

                   if (!page)

                            goto oom;

                  copy_user_highpage(page, new_page, address);///copy page

                   page_cache_release(new_page);

                   new_page = page;

                   anon = 1;

         }

…

                   if (anon) {

                            lru_cache_add_active(new_page);//将页插入LRU的活动链表

                            page_add_anon_rmap(new_page, vma, address);//将匿名页插入到反向映射数据结构

                   }

…

}

# free

             total       used       free     shared    buffers     cached

Mem:       1966220    1676428     289792          0     418900     705216

-/+ buffers/cache:     552312    1413908

Swap:      2104504     131084    1973420

# echo 1 > /proc/sys/vm/drop_caches

# free

             total       used       free     shared    buffers     cached

Mem:       1966220     597840    1368380          0        324      65852

-/+ buffers/cache:     531664    1434556

Swap:      2104504     131084    1973420