From: Mike Kravetz <mike.kravetz@oracle.com>
To: Mina Almasry <almasrymina@google.com>
Cc: shuah@kernel.org, rientjes@google.com, shakeelb@google.com,
gthelen@google.com, akpm@linux-foundation.org,
khalid.aziz@oracle.com, linux-kernel@vger.kernel.org,
linux-mm@kvack.org, linux-kselftest@vger.kernel.org,
cgroups@vger.kernel.org, aneesh.kumar@linux.vnet.ibm.com,
mkoutny@suse.com
Subject: Re: [PATCH v6 5/9] hugetlb: disable region_add file_region coalescing
Date: Mon, 21 Oct 2019 12:02:46 -0700 [thread overview]
Message-ID: <982efbbc-f795-5819-83a8-7d328537e070@oracle.com> (raw)
In-Reply-To: <20191013003024.215429-5-almasrymina@google.com>
On 10/12/19 5:30 PM, Mina Almasry wrote:
> A follow up patch in this series adds hugetlb cgroup uncharge info the
> file_region entries in resv->regions. The cgroup uncharge info may
> differ for different regions, so they can no longer be coalesced at
> region_add time. So, disable region coalescing in region_add in this
> patch.
>
> Behavior change:
>
> Say a resv_map exists like this [0->1], [2->3], and [5->6].
>
> Then a region_chg/add call comes in region_chg/add(f=0, t=5).
>
> Old code would generate resv->regions: [0->5], [5->6].
> New code would generate resv->regions: [0->1], [1->2], [2->3], [3->5],
> [5->6].
>
> Special care needs to be taken to handle the resv->adds_in_progress
> variable correctly. In the past, only 1 region would be added for every
> region_chg and region_add call. But now, each call may add multiple
> regions, so we can no longer increment adds_in_progress by 1 in region_chg,
> or decrement adds_in_progress by 1 after region_add or region_abort. Instead,
> region_chg calls add_reservation_in_range() to count the number of regions
> needed and allocates those, and that info is passed to region_add and
> region_abort to decrement adds_in_progress correctly.
>
> Signed-off-by: Mina Almasry <almasrymina@google.com>
>
> ---
>
> Changes in v6:
> - Fix bug in number of region_caches allocated by region_chg
>
> ---
> mm/hugetlb.c | 256 +++++++++++++++++++++++++++++----------------------
> 1 file changed, 147 insertions(+), 109 deletions(-)
>
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 4a60d7d44b4c3..f9c1947925bb9 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
<snip>
> -static long region_chg(struct resv_map *resv, long f, long t)
> +static long region_chg(struct resv_map *resv, long f, long t,
> + long *out_regions_needed)
> {
> + struct file_region *trg = NULL;
> long chg = 0;
>
> + /* Allocate the maximum number of regions we're going to need for this
> + * reservation. The maximum number of regions we're going to need is
> + * (t - f) / 2 + 1, which corresponds to a region with alternating
> + * reserved and unreserved pages.
> + */
> + *out_regions_needed = (t - f) / 2 + 1;
> +
> spin_lock(&resv->lock);
> -retry_locked:
> - resv->adds_in_progress++;
> +
> + resv->adds_in_progress += *out_regions_needed;
>
> /*
> * Check for sufficient descriptors in the cache to accommodate
> * the number of in progress add operations.
> */
> - if (resv->adds_in_progress > resv->region_cache_count) {
> - struct file_region *trg;
> -
> - VM_BUG_ON(resv->adds_in_progress - resv->region_cache_count > 1);
> + while (resv->region_cache_count < resv->adds_in_progress) {
> /* Must drop lock to allocate a new descriptor. */
> - resv->adds_in_progress--;
> spin_unlock(&resv->lock);
> -
> trg = kmalloc(sizeof(*trg), GFP_KERNEL);
> if (!trg)
> return -ENOMEM;
> @@ -393,9 +395,9 @@ static long region_chg(struct resv_map *resv, long f, long t)
> spin_lock(&resv->lock);
> list_add(&trg->link, &resv->region_cache);
> resv->region_cache_count++;
> - goto retry_locked;
> }
I know that I suggested allocating the worst case number of entries, but this
is going to be too much of a hit for existing hugetlbfs users. It is not
uncommon for DBs to have a shared areas in excess of 1TB mapped by hugetlbfs.
With this new scheme, the above while loop will allocate over a half million
file region entries and end up only using one.
I think we need to step back and come up with a different approach. Let me
give it some more thought before throwing out ideas that may waste more of
your time. Sorry.
--
Mike Kravetz
next prev parent reply other threads:[~2019-10-21 19:02 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-13 0:30 [PATCH v6 1/9] hugetlb_cgroup: Add hugetlb_cgroup reservation counter Mina Almasry
2019-10-13 0:30 ` [PATCH v6 2/9] hugetlb_cgroup: add interface for charge/uncharge hugetlb reservations Mina Almasry
2019-10-13 0:30 ` [PATCH v6 3/9] hugetlb_cgroup: add cgroup-v2 support Mina Almasry
2019-10-13 0:30 ` [PATCH v6 4/9] hugetlb_cgroup: add reservation accounting for private mappings Mina Almasry
2019-10-13 0:30 ` [PATCH v6 5/9] hugetlb: disable region_add file_region coalescing Mina Almasry
2019-10-21 19:02 ` Mike Kravetz [this message]
2019-10-21 19:29 ` Mina Almasry
2019-10-13 0:30 ` [PATCH v6 6/9] hugetlb_cgroup: add accounting for shared mappings Mina Almasry
2019-10-13 0:30 ` [PATCH v6 7/9] hugetlb_cgroup: support noreserve mappings Mina Almasry
2019-10-13 0:30 ` [PATCH v6 8/9] hugetlb_cgroup: Add hugetlb_cgroup reservation tests Mina Almasry
2019-10-13 0:30 ` [PATCH v6 9/9] hugetlb_cgroup: Add hugetlb_cgroup reservation docs Mina Almasry
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=982efbbc-f795-5819-83a8-7d328537e070@oracle.com \
--to=mike.kravetz@oracle.com \
--cc=akpm@linux-foundation.org \
--cc=almasrymina@google.com \
--cc=aneesh.kumar@linux.vnet.ibm.com \
--cc=cgroups@vger.kernel.org \
--cc=gthelen@google.com \
--cc=khalid.aziz@oracle.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-kselftest@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=mkoutny@suse.com \
--cc=rientjes@google.com \
--cc=shakeelb@google.com \
--cc=shuah@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).