On Thu 22-10-20 09:25:21, Rik van Riel wrote: > On Thu, 2020-10-22 at 10:15 +0200, Michal Hocko wrote: > > On Wed 21-10-20 23:48:46, Rik van Riel wrote: > > > The allocation flags of anonymous transparent huge pages can be > > > controlled > > > through the files in /sys/kernel/mm/transparent_hugepage/defrag, > > > which can > > > help the system from getting bogged down in the page reclaim and > > > compaction > > > code when many THPs are getting allocated simultaneously. > > > > > > However, the gfp_mask for shmem THP allocations were not limited by > > > those > > > configuration settings, and some workloads ended up with all CPUs > > > stuck > > > on the LRU lock in the page reclaim code, trying to allocate dozens > > > of > > > THPs simultaneously. > > > > > > This patch applies the same configurated limitation of THPs to > > > shmem > > > hugepage allocations, to prevent that from happening. > > > > > > This way a THP defrag setting of "never" or "defer+madvise" will > > > result > > > in quick allocation failures without direct reclaim when no 2MB > > > free > > > pages are available. > > > > I remmeber I wanted to unify this in the past as well. The patch got > > reverted in the end. It was a long story and I do not have time to > > read > > through lengthy discussions again. I do remember though that there > > were > > some objections pointing out that shmem has its own behavior which is > > controlled by the mount option - at least for the explicitly mounted > > shmems. I might misremember. > > That is not entirely true, though. > > THP has two main sysfs knobs: "enabled" and "defrag" > > The mount options > control the shmem equivalent options > for "enabled", but they do not do anything for the "defrag" > equivalent options. Yeah, the situation is quite messy :/ > This patch applies the "defrag" THP options to > shmem. I am not really objecting I just do remember some pushback. My previous attempt was to unify everything inside alloc_pages_vma IIRC. > > [...] > > > > > diff --git a/mm/shmem.c b/mm/shmem.c > > > index 537c137698f8..d1290eb508e5 100644 > > > --- a/mm/shmem.c > > > +++ b/mm/shmem.c > > > @@ -1545,8 +1545,11 @@ static struct page > > > *shmem_alloc_hugepage(gfp_t gfp, > > > return NULL; > > > > > > shmem_pseudo_vma_init(&pvma, info, hindex); > > > - page = alloc_pages_vma(gfp | __GFP_COMP | __GFP_NORETRY | > > > __GFP_NOWARN, > > > - HPAGE_PMD_ORDER, &pvma, 0, numa_node_id(), > > > true); > > > + /* Limit the gfp mask according to THP configuration. */ > > > + gfp |= __GFP_COMP | __GFP_NORETRY | __GFP_NOWARN; > > > > What is the reason for these when alloc_hugepage_direct_gfpmask > > provides > > the full mask? > > The mapping_gfp_mask for the shmem file might have additional > restrictions above and beyond the gfp mask returned by > alloc_hugepage_direct_gfpmask, and I am not sure we should just > ignore the mapping_gfp_mask. No, we shouldn't. But I do not see why you should be adding the above set of flags on top. > That is why this patch takes the union of both gfp masks. > > However, digging into things more, it looks like shmem inodes > always have the mapping gfp mask set to GFP_HIGHUSER_MOVABLE, > and it is never changed, so simply using the output from > alloc_hugepage_direct_gfpmask should be fine. > > I can do the patch either way. Just let me know what you prefer. I would just and the given gfp with alloc_hugepage_direct_gfpmask -- Michal Hocko SUSE Labs
