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Date: Fri, 03 Jul 2015 15:20:34 +0800
From: "Hillf Danton" <hillf.zj@...baba-inc.com>
To: "'Mike Kravetz'" <mike.kravetz@...cle.com>, <linux-mm@...ck.org>,
<linux-kernel@...r.kernel.org>, <linux-api@...r.kernel.org>
Cc: "'Dave Hansen'" <dave.hansen@...ux.intel.com>,
"'Naoya Horiguchi'" <n-horiguchi@...jp.nec.com>,
"'David Rientjes'" <rientjes@...gle.com>,
"'Hugh Dickins'" <hughd@...gle.com>,
"'Davidlohr Bueso'" <dave@...olabs.net>,
"'Aneesh Kumar'" <aneesh.kumar@...ux.vnet.ibm.com>,
"'Christoph Hellwig'" <hch@...radead.org>
Subject: Re: [PATCH 02/10] mm/hugetlb: add region_del() to delete a specific range of entries
> fallocate hole punch will want to remove a specific range of pages.
> The existing region_truncate() routine deletes all region/reserve
> map entries after a specified offset. region_del() will provide
> this same functionality if the end of region is specified as -1.
> Hence, region_del() can replace region_truncate().
>
> Unlike region_truncate(), region_del() can return an error in the
> rare case where it can not allocate memory for a region descriptor.
> This ONLY happens in the case where an existing region must be split.
> Current callers passing -1 as end of range will never experience
> this error and do not need to deal with error handling. Future
> callers of region_del() (such as fallocate hole punch) will need to
> handle this error.
>
> Signed-off-by: Mike Kravetz <mike.kravetz@...cle.com>
> ---
> mm/hugetlb.c | 101 ++++++++++++++++++++++++++++++++++++++++++++---------------
> 1 file changed, 75 insertions(+), 26 deletions(-)
>
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 189c0d7..e8c7f68 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -460,43 +460,92 @@ static void region_abort(struct resv_map *resv, long f, long t)
> }
>
> /*
> - * Truncate the reserve map at index 'end'. Modify/truncate any
> - * region which contains end. Delete any regions past end.
> - * Return the number of huge pages removed from the map.
> + * Delete the specified range [f, t) from the reserve map. If the
> + * t parameter is -1, this indicates that ALL regions after f should
> + * be deleted. Locate the regions which intersect [f, t) and either
> + * trim, delete or split the existing regions.
> + *
> + * Returns the number of huge pages deleted from the reserve map.
> + * In the normal case, the return value is zero or more. In the
> + * case where a region must be split, a new region descriptor must
> + * be allocated. If the allocation fails, -ENOMEM will be returned.
> + * NOTE: If the parameter t == -1, then we will never split a region
> + * and possibly return -ENOMEM. Callers specifying t == -1 do not
> + * need to check for -ENOMEM error.
> */
> -static long region_truncate(struct resv_map *resv, long end)
> +static long region_del(struct resv_map *resv, long f, long t)
> {
> struct list_head *head = &resv->regions;
> struct file_region *rg, *trg;
> - long chg = 0;
> + struct file_region *nrg = NULL;
> + long del = 0;
>
> + if (t == -1)
> + t = LONG_MAX;
Why not use
> +retry:
> spin_lock(&resv->lock);
> - /* Locate the region we are either in or before. */
> - list_for_each_entry(rg, head, link)
> - if (end <= rg->to)
> + list_for_each_entry_safe(rg, trg, head, link) {
> + if (rg->to <= f)
> + continue;
> + if (rg->from >= t)
> break;
> - if (&rg->link == head)
> - goto out;
>
> - /* If we are in the middle of a region then adjust it. */
> - if (end > rg->from) {
> - chg = rg->to - end;
> - rg->to = end;
> - rg = list_entry(rg->link.next, typeof(*rg), link);
> - }
> + if (f > rg->from && t < rg->to) { /* Must split region */
> + /*
> + * Check for an entry in the cache before dropping
> + * lock and attempting allocation.
> + */
> + if (!nrg &&
> + resv->rgn_cache_count > resv->adds_in_progress) {
> + nrg = list_first_entry(&resv->rgn_cache,
> + struct file_region,
> + link);
> + list_del(&nrg->link);
> + resv->rgn_cache_count--;
> + }
>
> - /* Drop any remaining regions. */
> - list_for_each_entry_safe(rg, trg, rg->link.prev, link) {
> - if (&rg->link == head)
> + if (!nrg) {
> + spin_unlock(&resv->lock);
> + nrg = kmalloc(sizeof(*nrg), GFP_KERNEL);
> + if (!nrg)
> + return -ENOMEM;
> + goto retry;
> + }
> +
> + del += t - f;
> +
> + /* New entry for end of split region */
> + nrg->from = t;
> + nrg->to = rg->to;
> + INIT_LIST_HEAD(&nrg->link);
> +
> + /* Original entry is trimmed */
> + rg->to = f;
> +
> + list_add(&nrg->link, &rg->link);
> + nrg = NULL;
> break;
> - chg += rg->to - rg->from;
> - list_del(&rg->link);
> - kfree(rg);
> + }
> +
> + if (f <= rg->from && t >= rg->to) { /* Remove entire region */
> + del += rg->to - rg->from;
> + list_del(&rg->link);
> + kfree(rg);
> + continue;
> + }
> +
> + if (f <= rg->from) { /* Trim beginning of region */
> + del += t - rg->from;
> + rg->from = t;
> + } else { /* Trim end of region */
> + del += rg->to - f;
> + rg->to = f;
> + }
> }
>
> -out:
> spin_unlock(&resv->lock);
> - return chg;
> + kfree(nrg);
> + return del;
> }
>
> /*
> @@ -647,7 +696,7 @@ void resv_map_release(struct kref *ref)
> struct file_region *rg, *trg;
>
> /* Clear out any active regions before we release the map. */
> - region_truncate(resv_map, 0);
> + region_del(resv_map, 0, -1);
LONG_MAX is not selected, why?
>
> /* ... and any entries left in the cache */
> list_for_each_entry_safe(rg, trg, head, link)
> @@ -3868,7 +3917,7 @@ void hugetlb_unreserve_pages(struct inode *inode, long offset, long freed)
> long gbl_reserve;
>
> if (resv_map)
> - chg = region_truncate(resv_map, offset);
> + chg = region_del(resv_map, offset, -1);
> spin_lock(&inode->i_lock);
> inode->i_blocks -= (blocks_per_huge_page(h) * freed);
> spin_unlock(&inode->i_lock);
> --
> 2.1.0
--
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