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writeback: separate out domain_dirty_limits() 

global_dirty_limits() calculates thresh and bg_thresh (confusingly
called *pdirty and *pbackground in the function) assuming
global_wb_domain; however, cgroup writeback support requires
considering per-memcg wb_domain too.

This patch separates out domain_dirty_limits() which takes
dirty_throttle_control out of global_dirty_limits().  As thresh and
bg_thresh calculation needs the amount of dirtyable memory in the
domain, dirty_throttle_control->avail is added.  The new function
calculates the two thresholds and store them directly in the
dirty_throttle_control.

Also, as memcg domains can't follow vm_dirty_bytes and
dirty_background_bytes settings directly.  If those are set and
domain_dirty_limits() is invoked for a !global domain, the settings
are translated to ratios by scaling them against globally available
memory.  dirty_throttle_control->gdtc is added to enable this when
CONFIG_CGROUP_WRITEBACK.

global_dirty_limits() is now a thin wrapper around
domain_dirty_limits() and balance_dirty_pages() is updated to use the
new function too.

This patch doesn't introduce any behavioral changes.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Jan Kara <jack@suse.cz>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Greg Thelen <gthelen@google.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
This commit is contained in:
Tejun Heo 2015-05-22 18:23:30 -04:00 committed by Jens Axboe
parent c7981433ef
commit 9fc3a43e17
1 changed files with 91 additions and 30 deletions
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121
mm/page-writeback.c
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@ -128,10 +128,12 @@ struct wb_domain global_wb_domain;
struct dirty_throttle_control {
#ifdef CONFIG_CGROUP_WRITEBACK
struct wb_domain *dom;
struct dirty_throttle_control *gdtc; /* only set in memcg dtc's */
#endif
struct bdi_writeback *wb;
struct fprop_local_percpu *wb_completions;
unsigned long avail; /* dirtyable */
unsigned long dirty; /* file_dirty + write + nfs */
unsigned long thresh; /* dirty threshold */
unsigned long bg_thresh; /* dirty background threshold */
@ -157,12 +159,18 @@ struct dirty_throttle_control {
#define GDTC_INIT(__wb) .dom = &global_wb_domain, \
DTC_INIT_COMMON(__wb)
#define GDTC_INIT_NO_WB .dom = &global_wb_domain
static struct wb_domain *dtc_dom(struct dirty_throttle_control *dtc)
{
return dtc->dom;
}
static struct dirty_throttle_control *mdtc_gdtc(struct dirty_throttle_control *mdtc)
{
return mdtc->gdtc;
}
static void wb_min_max_ratio(struct bdi_writeback *wb,
unsigned long *minp, unsigned long *maxp)
{
@ -193,12 +201,18 @@ static void wb_min_max_ratio(struct bdi_writeback *wb,
#else /* CONFIG_CGROUP_WRITEBACK */
#define GDTC_INIT(__wb) DTC_INIT_COMMON(__wb)
#define GDTC_INIT_NO_WB
static struct wb_domain *dtc_dom(struct dirty_throttle_control *dtc)
{
return &global_wb_domain;
}
static struct dirty_throttle_control *mdtc_gdtc(struct dirty_throttle_control *mdtc)
{
return NULL;
}
static void wb_min_max_ratio(struct bdi_writeback *wb,
unsigned long *minp, unsigned long *maxp)
{
@ -303,42 +317,88 @@ static unsigned long global_dirtyable_memory(void)
return x + 1; /* Ensure that we never return 0 */
}
/*
* global_dirty_limits - background-writeback and dirty-throttling thresholds
/**
* domain_dirty_limits - calculate thresh and bg_thresh for a wb_domain
* @dtc: dirty_throttle_control of interest
*
* Calculate the dirty thresholds based on sysctl parameters
* - vm.dirty_background_ratio or vm.dirty_background_bytes
* - vm.dirty_ratio or vm.dirty_bytes
* The dirty limits will be lifted by 1/4 for PF_LESS_THROTTLE (ie. nfsd) and
* Calculate @dtc->thresh and ->bg_thresh considering
* vm_dirty_{bytes|ratio} and dirty_background_{bytes|ratio}. The caller
* must ensure that @dtc->avail is set before calling this function. The
* dirty limits will be lifted by 1/4 for PF_LESS_THROTTLE (ie. nfsd) and
* real-time tasks.
*/
static void domain_dirty_limits(struct dirty_throttle_control *dtc)
{
const unsigned long available_memory = dtc->avail;
struct dirty_throttle_control *gdtc = mdtc_gdtc(dtc);
unsigned long bytes = vm_dirty_bytes;
unsigned long bg_bytes = dirty_background_bytes;
unsigned long ratio = vm_dirty_ratio;
unsigned long bg_ratio = dirty_background_ratio;
unsigned long thresh;
unsigned long bg_thresh;
struct task_struct *tsk;
/* gdtc is !NULL iff @dtc is for memcg domain */
if (gdtc) {
unsigned long global_avail = gdtc->avail;
/*
* The byte settings can't be applied directly to memcg
* domains. Convert them to ratios by scaling against
* globally available memory.
*/
if (bytes)
ratio = min(DIV_ROUND_UP(bytes, PAGE_SIZE) * 100 /
global_avail, 100UL);
if (bg_bytes)
bg_ratio = min(DIV_ROUND_UP(bg_bytes, PAGE_SIZE) * 100 /
global_avail, 100UL);
bytes = bg_bytes = 0;
}
if (bytes)
thresh = DIV_ROUND_UP(bytes, PAGE_SIZE);
else
thresh = (ratio * available_memory) / 100;
if (bg_bytes)
bg_thresh = DIV_ROUND_UP(bg_bytes, PAGE_SIZE);
else
bg_thresh = (bg_ratio * available_memory) / 100;
if (bg_thresh >= thresh)
bg_thresh = thresh / 2;
tsk = current;
if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) {
bg_thresh += bg_thresh / 4;
thresh += thresh / 4;
}
dtc->thresh = thresh;
dtc->bg_thresh = bg_thresh;
/* we should eventually report the domain in the TP */
if (!gdtc)
trace_global_dirty_state(bg_thresh, thresh);
}
/**
* global_dirty_limits - background-writeback and dirty-throttling thresholds
* @pbackground: out parameter for bg_thresh
* @pdirty: out parameter for thresh
*
* Calculate bg_thresh and thresh for global_wb_domain. See
* domain_dirty_limits() for details.
*/
void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty)
{
const unsigned long available_memory = global_dirtyable_memory();
unsigned long background;
unsigned long dirty;
struct task_struct *tsk;
struct dirty_throttle_control gdtc = { GDTC_INIT_NO_WB };
if (vm_dirty_bytes)
dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE);
else
dirty = (vm_dirty_ratio * available_memory) / 100;
gdtc.avail = global_dirtyable_memory();
domain_dirty_limits(&gdtc);
if (dirty_background_bytes)
background = DIV_ROUND_UP(dirty_background_bytes, PAGE_SIZE);
else
background = (dirty_background_ratio * available_memory) / 100;
if (background >= dirty)
background = dirty / 2;
tsk = current;
if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) {
background += background / 4;
dirty += dirty / 4;
}
*pbackground = background;
*pdirty = dirty;
trace_global_dirty_state(background, dirty);
*pbackground = gdtc.bg_thresh;
*pdirty = gdtc.thresh;
}
/**
@ -1421,9 +1481,10 @@ static void balance_dirty_pages(struct address_space *mapping,
*/
nr_reclaimable = global_page_state(NR_FILE_DIRTY) +
global_page_state(NR_UNSTABLE_NFS);
gdtc->avail = global_dirtyable_memory();
gdtc->dirty = nr_reclaimable + global_page_state(NR_WRITEBACK);
global_dirty_limits(&gdtc->bg_thresh, &gdtc->thresh);
domain_dirty_limits(gdtc);
if (unlikely(strictlimit)) {
wb_dirty_limits(gdtc);