lkml.org 
[lkml]   [2016]   [Oct]   [7]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    Date
    From
    SubjectRe: [RFC PATCH] mm, compaction: allow compaction for GFP_NOFS requests
    On Fri 07-10-16 07:27:37, Vlastimil Babka wrote:
    [...]
    > > diff --git a/mm/compaction.c b/mm/compaction.c
    > > index badb92bf14b4..07254a73ee32 100644
    > > --- a/mm/compaction.c
    > > +++ b/mm/compaction.c
    > > @@ -834,6 +834,13 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
    > > page_count(page) > page_mapcount(page))
    > > goto isolate_fail;
    > >
    > > + /*
    > > + * Only allow to migrate anonymous pages in GFP_NOFS context
    > > + * because those do not depend on fs locks.
    > > + */
    > > + if (!(cc->gfp_mask & __GFP_FS) && page_mapping(page))
    > > + goto isolate_fail;
    >
    > Unless page can acquire a page_mapping between this check and migration, I
    > don't see a problem with allowing this.

    It can be become swapcache but I guess this should be OK. We do not
    allow to get here with GFP_NOIO and migrating swapcache pages in NOFS
    mode should be OK AFAICS.

    > But make sure you don't break kcompactd and manual compaction from /proc, as
    > they don't currently set cc->gfp_mask. Looks like until now it was only used
    > to determine direct compactor's migratetype which is irrelevant in those
    > contexts.

    OK, I see. This is really subtle. One way to go would be to provide a
    fake gfp_mask for them. How does the following look to you?
    ---
    diff --git a/mm/compaction.c b/mm/compaction.c
    index 557c165b63ad..d1d90e96ef4b 100644
    --- a/mm/compaction.c
    +++ b/mm/compaction.c
    @@ -1779,6 +1779,7 @@ static void compact_node(int nid)
    .mode = MIGRATE_SYNC,
    .ignore_skip_hint = true,
    .whole_zone = true,
    + .gfp_mask = GFP_KERNEL,
    };


    @@ -1904,6 +1905,7 @@ static void kcompactd_do_work(pg_data_t *pgdat)
    .classzone_idx = pgdat->kcompactd_classzone_idx,
    .mode = MIGRATE_SYNC_LIGHT,
    .ignore_skip_hint = true,
    + .gfp_mask = GFP_KERNEL,

    };
    trace_mm_compaction_kcompactd_wake(pgdat->node_id, cc.order,
    --
    Michal Hocko
    SUSE Labs
    \
     
     \ /
      Last update: 2016-10-07 08:51    [W:4.658 / U:0.008 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site