• Vlastimil Babka's avatar
    mm, slab: combine kmalloc_caches and kmalloc_dma_caches · cc252eae
    Vlastimil Babka authored
    Patch series "kmalloc-reclaimable caches", v4.
    
    As discussed at LSF/MM [1] here's a patchset that introduces
    kmalloc-reclaimable caches (more details in the second patch) and uses
    them for dcache external names.  That allows us to repurpose the
    NR_INDIRECTLY_RECLAIMABLE_BYTES counter later in the series.
    
    With patch 3/6, dcache external names are allocated from kmalloc-rcl-*
    caches, eliminating the need for manual accounting.  More importantly, it
    also ensures the reclaimable kmalloc allocations are grouped in pages
    separate from the regular kmalloc allocations.  The need for proper
    accounting of dcache external names has shown it's easy for misbehaving
    process to allocate lots of them, causing premature OOMs.  Without the
    added grouping, it's likely that a similar workload can interleave the
    dcache external names allocations with regular kmalloc allocations (note:
    I haven't searched myself for an example of such regular kmalloc
    allocation, but I would be very surprised if there wasn't some).  A
    pathological case would be e.g.  one 64byte regular allocations with 63
    external dcache names in a page (64x64=4096), which means the page is not
    freed even after reclaiming after all dcache names, and the process can
    thus "steal" the whole page with single 64byte allocation.
    
    If other kmalloc users similar to dcache external names become identified,
    they can also benefit from the new functionality simply by adding
    __GFP_RECLAIMABLE to the kmalloc calls.
    
    Side benefits of the patchset (that could be also merged separately)
    include removed branch for detecting __GFP_DMA kmalloc(), and shortening
    kmalloc cache names in /proc/slabinfo output.  The latter is potentially
    an ABI break in case there are tools parsing the names and expecting the
    values to be in bytes.
    
    This is how /proc/slabinfo looks like after booting in virtme:
    
    ...
    kmalloc-rcl-4M         0      0 4194304    1 1024 : tunables    1    1    0 : slabdata      0      0      0
    ...
    kmalloc-rcl-96         7     32    128   32    1 : tunables  120   60    8 : slabdata      1      1      0
    kmalloc-rcl-64        25    128     64   64    1 : tunables  120   60    8 : slabdata      2      2      0
    kmalloc-rcl-32         0      0     32  124    1 : tunables  120   60    8 : slabdata      0      0      0
    kmalloc-4M             0      0 4194304    1 1024 : tunables    1    1    0 : slabdata      0      0      0
    kmalloc-2M             0      0 2097152    1  512 : tunables    1    1    0 : slabdata      0      0      0
    kmalloc-1M             0      0 1048576    1  256 : tunables    1    1    0 : slabdata      0      0      0
    ...
    
    /proc/vmstat with renamed nr_indirectly_reclaimable_bytes counter:
    
    ...
    nr_slab_reclaimable 2817
    nr_slab_unreclaimable 1781
    ...
    nr_kernel_misc_reclaimable 0
    ...
    
    /proc/meminfo with new KReclaimable counter:
    
    ...
    Shmem:               564 kB
    KReclaimable:      11260 kB
    Slab:              18368 kB
    SReclaimable:      11260 kB
    SUnreclaim:         7108 kB
    KernelStack:        1248 kB
    ...
    
    This patch (of 6):
    
    The kmalloc caches currently mainain separate (optional) array
    kmalloc_dma_caches for __GFP_DMA allocations.  There are tests for
    __GFP_DMA in the allocation hotpaths.  We can avoid the branches by
    combining kmalloc_caches and kmalloc_dma_caches into a single
    two-dimensional array where the outer dimension is cache "type".  This
    will also allow to add kmalloc-reclaimable caches as a third type.
    
    Link: http://lkml.kernel.org/r/20180731090649.16028-2-vbabka@suse.czSigned-off-by: default avatarVlastimil Babka <vbabka@suse.cz>
    Acked-by: default avatarMel Gorman <mgorman@techsingularity.net>
    Acked-by: default avatarChristoph Lameter <cl@linux.com>
    Acked-by: default avatarRoman Gushchin <guro@fb.com>
    Cc: Michal Hocko <mhocko@kernel.org>
    Cc: Johannes Weiner <hannes@cmpxchg.org>
    Cc: David Rientjes <rientjes@google.com>
    Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
    Cc: Matthew Wilcox <willy@infradead.org>
    Cc: Laura Abbott <labbott@redhat.com>
    Cc: Sumit Semwal <sumit.semwal@linaro.org>
    Cc: Vijayanand Jitta <vjitta@codeaurora.org>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    cc252eae
slab.c 111 KB