[CRIU] [RFC 1/3] pagemap-cache: Introduce engine
Andrew Vagin
avagin at parallels.com
Fri Feb 14 07:03:06 PST 2014
On Fri, Feb 14, 2014 at 12:41:11AM +0400, Cyrill Gorcunov wrote:
> Pavel reported that in case if there a big number
> of small vmas present in the dumpee we're reading
> /proc/pid/pagemap too frequently.
>
> To speedup this procedue we inroduce pagemap cache.
>
> The interface is:
> - pmc_init/pmc_fini for cache initialization and freeing
> - pmc_get_pme to retrieve specific PME from cache
>
> Reported-by: Pavel Emelyanov <xemul at parallels.com>
> Signed-off-by: Cyrill Gorcunov <gorcunov at openvz.org>
> ---
> Makefile.crtools | 1 +
> include/pagemap-cache.h | 40 +++++++++++++
> pagemap-cache.c | 150 ++++++++++++++++++++++++++++++++++++++++++++++++
> 3 files changed, 191 insertions(+)
> create mode 100644 include/pagemap-cache.h
> create mode 100644 pagemap-cache.c
>
> diff --git a/Makefile.crtools b/Makefile.crtools
> index 374cd8570289..6effc3e0958b 100644
> --- a/Makefile.crtools
> +++ b/Makefile.crtools
> @@ -53,6 +53,7 @@ obj-y += file-lock.o
> obj-y += page-pipe.o
> obj-y += page-xfer.o
> obj-y += page-read.o
> +obj-y += pagemap-cache.o
> obj-y += kerndat.o
> obj-y += stats.o
> obj-y += string.o
> diff --git a/include/pagemap-cache.h b/include/pagemap-cache.h
> new file mode 100644
> index 000000000000..9fe03f17d97f
> --- /dev/null
> +++ b/include/pagemap-cache.h
> @@ -0,0 +1,40 @@
> +#ifndef __CR_PAGEMAP_H__
> +#define __CR_PAGEMAP_H__
> +
> +#include <sys/types.h>
> +#include "asm/types.h"
> +
> +#include "list.h"
> +
> +struct vma_area;
> +
> +/* To carry up to 2M of physical memory */
> +#define PMC_SHIFT (21)
> +#define PMC_SIZE (1ul << PMC_SHIFT)
> +#define PMC_MASK (~(PMC_SIZE - 1))
> +#define PMC_SIZE_GAP (PMC_SIZE / 4)
> +
> +#define PAGEMAP_LEN(pages) ((pages) * sizeof(u64))
> +#define PAGEMAP_PFN(addr) ((addr) / PAGE_SIZE)
> +
> +#define PAGEMAP_PFN_OFF(addr) (PAGEMAP_PFN(addr) * sizeof(u64))
> +
> +#define PAGEMAP_PME_ERR ((u64)-1)
> +
> +typedef struct {
> + pid_t pid; /* which process it belongs */
> + unsigned long start; /* start of area */
> + unsigned long end; /* end of area */
> + struct list_head *vma_head; /* list head of VMAs we're serving */
> + u64 *map; /* local buffer */
> + size_t map_len; /* length of a buffer */
> + int fd; /* file to read PMs from */
> +} pmc_t;
> +
> +#define PMC_INIT (pmc_t){ }
> +
> +extern int pmc_init(pmc_t *pmc, pid_t pid, struct list_head *vma_head, size_t size);
> +extern u64 pmc_get_pme(pmc_t *pmc, struct vma_area *vma, unsigned long addr);
> +extern void pmc_fini(pmc_t *pmc);
> +
> +#endif /* __CR_PAGEMAP_H__ */
> diff --git a/pagemap-cache.c b/pagemap-cache.c
> new file mode 100644
> index 000000000000..ddeca9a12518
> --- /dev/null
> +++ b/pagemap-cache.c
> @@ -0,0 +1,150 @@
> +#include <unistd.h>
> +#include <fcntl.h>
> +
> +#include "pagemap-cache.h"
> +#include "compiler.h"
> +#include "xmalloc.h"
> +#include "util.h"
> +#include "log.h"
> +#include "vma.h"
> +
> +#undef LOG_PREFIX
> +#define LOG_PREFIX "pagemap-cache: "
> +
> +static inline void pmc_reset(pmc_t *pmc)
> +{
> + memzero(pmc, sizeof(*pmc));
> + pmc->fd = -1;
> +}
> +
> +static inline void pmc_zap(pmc_t *pmc)
> +{
> + pmc->start = pmc->end = 0;
> +}
> +
> +int pmc_init(pmc_t *pmc, pid_t pid, struct list_head *vma_head, size_t size)
> +{
> + size_t map_size = max(size, PMC_SIZE);
> + pmc_reset(pmc);
> +
> + BUG_ON(!vma_head);
> +
> + pmc->pid = pid;
> + pmc->fd = open_proc(pid, "pagemap");
> + pmc->map_len = PAGEMAP_LEN(PAGEMAP_PFN(map_size));
> + pmc->map = xmalloc(pmc->map_len);
> + pmc->vma_head = vma_head;
> +
> + if (!pmc->map || pmc->fd < 0) {
> + pr_err("Failed to init pagemap for %d\n", pid);
> + pmc_fini(pmc);
> + return -1;
> + }
> +
> + pr_debug("created for pid %d (takes %zu bytes)\n", pid, pmc->map_len);
> +
> + return 0;
> +}
> +
> +static u64 __pmc_get_pme(pmc_t *pmc, unsigned long addr)
> +{
> + if (likely(pmc->start <= addr && pmc->end > addr))
> + return pmc->map[PAGEMAP_PFN(addr - pmc->start)];
> + return PAGEMAP_PME_ERR;
> +}
> +
> +static int pmc_fill_cache(pmc_t *pmc, struct vma_area *vma)
> +{
> + unsigned long low = vma->e->start & PMC_MASK;
> + unsigned long high = low + PMC_SIZE;
> + size_t len = vma_area_len(vma);
> + size_t size_map;
> +
> + pmc->start = vma->e->start;
> + pmc->end = vma->e->end;
> +
> + pr_debug("filling VMA %lx-%lx (%luK) [l:%lx h:%lx]\n",
> + vma->e->start, vma->e->end, len >> 10, low, high);
> +
> + /*
> + * If we meet a small VMA, lets try to fit 2M cache
> + * window at least 75% full, otherwise left as a plain
> + * "one vma at a time" read. Note the VMAs in cache must
> + * fit in solid manner, iow -- either the whole vma fits
> + * the cache window, either plain read is used.
> + *
> + * The benefit (apart redusing the number of read() calls)
> + * is to keep in kernel THP lock as less as possible.
> + */
> + if (len < PMC_SIZE && (vma->e->start - low) < PMC_SIZE_GAP) {
> + size_t size_cov = len;
> + size_t nr_vmas = 1;
> +
> + pr_debug("\t%16lx-%-16lx nr:%-5zu cov:%zu\n",
> + vma->e->start, vma->e->end, nr_vmas, size_cov);
> +
> + list_for_each_entry_continue(vma, pmc->vma_head, list) {
> + if (vma->e->start > high || vma->e->end > high)
> + break;
> +
> + BUG_ON(vma->e->start < low);
> + size_cov += vma_area_len(vma);
> + nr_vmas++;
> +
> + pr_debug("\t%16lx-%-16lx nr:%-5zu cov:%zu\n",
> + vma->e->start, vma->e->end, nr_vmas, size_cov);
> + }
> +
> + if (size_cov > (PMC_SIZE - PMC_SIZE_GAP) && nr_vmas > 1) {
> + pmc->start = low;
> + pmc->end = high;
> + pr_debug("\tcache mode [l:%lx h:%lx]\n", pmc->start, pmc->end);
> + } else
> + pr_debug("\tsimple mode [l:%lx h:%lx]\n", pmc->start, pmc->end);
> + }
> +
> + size_map = PAGEMAP_LEN(PAGEMAP_PFN(pmc->end - pmc->start));
> + BUG_ON(pmc->map_len < size_map);
> +
> + if (pread(pmc->fd, pmc->map, size_map, PAGEMAP_PFN_OFF(pmc->start)) != size_map) {
> + pmc_zap(pmc);
> + pr_perror("Can't read %d's pagemap file", pmc->pid);
> + return -1;
> + }
> +
> + return 0;
> +}
> +
> +u64 pmc_get_pme(pmc_t *pmc, struct vma_area *vma, unsigned long addr)
Why do we need to call pmc_get_pme for each page? The cache contains pfn
for all pages of one vma or nothing, doesn't it?
> +{
> + u64 pme;
> +
> + BUG_ON(addr < vma->e->start || addr > vma->e->end);
> +
> + /*
> + * Best case -- cache hit.
> + */
> + pme = __pmc_get_pme(pmc, addr);
> + if (likely(pme != PAGEMAP_PME_ERR))
> + return pme;
> +
> + /*
> + * Cache miss, refill the cache.
> + */
> + if (pmc_fill_cache(pmc, vma)) {
> + pr_err("Failed to fill cache for %d (%lx)\n", pmc->pid, addr);
> + return PAGEMAP_PME_ERR;
> + }
> +
> + /*
> + * It must be a cache hit.
> + */
> + return __pmc_get_pme(pmc, addr);
> +}
> +
> +void pmc_fini(pmc_t *pmc)
> +{
> + close_safe(&pmc->fd);
> + xfree(pmc->map);
> + pmc_reset(pmc);
> +}
> --
> 1.8.3.1
>
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