Revision 03049269de433cb5fe2859be9ae4469ceb1163ed authored by Michal Hocko on 25 March 2016, 21:20:33 UTC, committed by Linus Torvalds on 25 March 2016, 23:37:42 UTC
wake_oom_reaper has allowed only 1 oom victim to be queued. The main reason for that was the simplicity as other solutions would require some way of queuing. The current approach is racy and that was deemed sufficient as the oom_reaper is considered a best effort approach to help with oom handling when the OOM victim cannot terminate in a reasonable time. The race could lead to missing an oom victim which can get stuck out_of_memory wake_oom_reaper cmpxchg // OK oom_reaper oom_reap_task __oom_reap_task oom_victim terminates atomic_inc_not_zero // fail out_of_memory wake_oom_reaper cmpxchg // fails task_to_reap = NULL This race requires 2 OOM invocations in a short time period which is not very likely but certainly not impossible. E.g. the original victim might have not released a lot of memory for some reason. The situation would improve considerably if wake_oom_reaper used a more robust queuing. This is what this patch implements. This means adding oom_reaper_list list_head into task_struct (eat a hole before embeded thread_struct for that purpose) and a oom_reaper_lock spinlock for queuing synchronization. wake_oom_reaper will then add the task on the queue and oom_reaper will dequeue it. Signed-off-by: Michal Hocko <mhocko@suse.com> Cc: Vladimir Davydov <vdavydov@virtuozzo.com> Cc: Andrea Argangeli <andrea@kernel.org> Cc: David Rientjes <rientjes@google.com> Cc: Hugh Dickins <hughd@google.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Mel Gorman <mgorman@suse.de> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Rik van Riel <riel@redhat.com> Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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sg_split.c
/*
* Copyright (C) 2015 Robert Jarzmik <robert.jarzmik@free.fr>
*
* Scatterlist splitting helpers.
*
* This source code is licensed under the GNU General Public License,
* Version 2. See the file COPYING for more details.
*/
#include <linux/scatterlist.h>
#include <linux/slab.h>
struct sg_splitter {
struct scatterlist *in_sg0;
int nents;
off_t skip_sg0;
unsigned int length_last_sg;
struct scatterlist *out_sg;
};
static int sg_calculate_split(struct scatterlist *in, int nents, int nb_splits,
off_t skip, const size_t *sizes,
struct sg_splitter *splitters, bool mapped)
{
int i;
unsigned int sglen;
size_t size = sizes[0], len;
struct sg_splitter *curr = splitters;
struct scatterlist *sg;
for (i = 0; i < nb_splits; i++) {
splitters[i].in_sg0 = NULL;
splitters[i].nents = 0;
}
for_each_sg(in, sg, nents, i) {
sglen = mapped ? sg_dma_len(sg) : sg->length;
if (skip > sglen) {
skip -= sglen;
continue;
}
len = min_t(size_t, size, sglen - skip);
if (!curr->in_sg0) {
curr->in_sg0 = sg;
curr->skip_sg0 = skip;
}
size -= len;
curr->nents++;
curr->length_last_sg = len;
while (!size && (skip + len < sglen) && (--nb_splits > 0)) {
curr++;
size = *(++sizes);
skip += len;
len = min_t(size_t, size, sglen - skip);
curr->in_sg0 = sg;
curr->skip_sg0 = skip;
curr->nents = 1;
curr->length_last_sg = len;
size -= len;
}
skip = 0;
if (!size && --nb_splits > 0) {
curr++;
size = *(++sizes);
}
if (!nb_splits)
break;
}
return (size || !splitters[0].in_sg0) ? -EINVAL : 0;
}
static void sg_split_phys(struct sg_splitter *splitters, const int nb_splits)
{
int i, j;
struct scatterlist *in_sg, *out_sg;
struct sg_splitter *split;
for (i = 0, split = splitters; i < nb_splits; i++, split++) {
in_sg = split->in_sg0;
out_sg = split->out_sg;
for (j = 0; j < split->nents; j++, out_sg++) {
*out_sg = *in_sg;
if (!j) {
out_sg->offset += split->skip_sg0;
out_sg->length -= split->skip_sg0;
} else {
out_sg->offset = 0;
}
sg_dma_address(out_sg) = 0;
sg_dma_len(out_sg) = 0;
in_sg = sg_next(in_sg);
}
out_sg[-1].length = split->length_last_sg;
sg_mark_end(out_sg - 1);
}
}
static void sg_split_mapped(struct sg_splitter *splitters, const int nb_splits)
{
int i, j;
struct scatterlist *in_sg, *out_sg;
struct sg_splitter *split;
for (i = 0, split = splitters; i < nb_splits; i++, split++) {
in_sg = split->in_sg0;
out_sg = split->out_sg;
for (j = 0; j < split->nents; j++, out_sg++) {
sg_dma_address(out_sg) = sg_dma_address(in_sg);
sg_dma_len(out_sg) = sg_dma_len(in_sg);
if (!j) {
sg_dma_address(out_sg) += split->skip_sg0;
sg_dma_len(out_sg) -= split->skip_sg0;
}
in_sg = sg_next(in_sg);
}
sg_dma_len(--out_sg) = split->length_last_sg;
}
}
/**
* sg_split - split a scatterlist into several scatterlists
* @in: the input sg list
* @in_mapped_nents: the result of a dma_map_sg(in, ...), or 0 if not mapped.
* @skip: the number of bytes to skip in the input sg list
* @nb_splits: the number of desired sg outputs
* @split_sizes: the respective size of each output sg list in bytes
* @out: an array where to store the allocated output sg lists
* @out_mapped_nents: the resulting sg lists mapped number of sg entries. Might
* be NULL if sglist not already mapped (in_mapped_nents = 0)
* @gfp_mask: the allocation flag
*
* This function splits the input sg list into nb_splits sg lists, which are
* allocated and stored into out.
* The @in is split into :
* - @out[0], which covers bytes [@skip .. @skip + @split_sizes[0] - 1] of @in
* - @out[1], which covers bytes [@skip + split_sizes[0] ..
* @skip + @split_sizes[0] + @split_sizes[1] -1]
* etc ...
* It will be the caller's duty to kfree() out array members.
*
* Returns 0 upon success, or error code
*/
int sg_split(struct scatterlist *in, const int in_mapped_nents,
const off_t skip, const int nb_splits,
const size_t *split_sizes,
struct scatterlist **out, int *out_mapped_nents,
gfp_t gfp_mask)
{
int i, ret;
struct sg_splitter *splitters;
splitters = kcalloc(nb_splits, sizeof(*splitters), gfp_mask);
if (!splitters)
return -ENOMEM;
ret = sg_calculate_split(in, sg_nents(in), nb_splits, skip, split_sizes,
splitters, false);
if (ret < 0)
goto err;
ret = -ENOMEM;
for (i = 0; i < nb_splits; i++) {
splitters[i].out_sg = kmalloc_array(splitters[i].nents,
sizeof(struct scatterlist),
gfp_mask);
if (!splitters[i].out_sg)
goto err;
}
/*
* The order of these 3 calls is important and should be kept.
*/
sg_split_phys(splitters, nb_splits);
ret = sg_calculate_split(in, in_mapped_nents, nb_splits, skip,
split_sizes, splitters, true);
if (ret < 0)
goto err;
sg_split_mapped(splitters, nb_splits);
for (i = 0; i < nb_splits; i++) {
out[i] = splitters[i].out_sg;
if (out_mapped_nents)
out_mapped_nents[i] = splitters[i].nents;
}
kfree(splitters);
return 0;
err:
for (i = 0; i < nb_splits; i++)
kfree(splitters[i].out_sg);
kfree(splitters);
return ret;
}
EXPORT_SYMBOL(sg_split);
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