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RE: [PATCH] storvsc: do not assume SG list is continuous when doing bounce buffers (for 4.1 stable only)

From Long Li <longli@microsoft.com>
Newsgroups linux.kernel
Subject RE: [PATCH] storvsc: do not assume SG list is continuous when doing bounce buffers (for 4.1 stable only)
Date 2017-08-22 21:20 +0200
Message-ID <uhmSu-6HP-9@gated-at.bofh.it> (permalink)
References <uha4V-6ko-3@gated-at.bofh.it> <uhaRj-6SH-1@gated-at.bofh.it>
Organization linux.* mail to news gateway

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> Wouldn't it make sense to backport the changes to set the virt_boundary
> (which probably still is the SG_GAPS flag in such an old kernel)?

We can make storvsc use SG_GAPS. But the following patch is missing in 4.1 stable block layer to make this work on some I/O situations. Backporting is more difficult and affect other code.

commit 5e7c4274a70aa2d6f485996d0ca1dad52d0039ca
Author: Jens Axboe <axboe@fb.com>
Date:   Thu Sep 3 19:28:20 2015 +0300

    block: Check for gaps on front and back merges
    
    We are checking for gaps to previous bio_vec, which can
    only detect back merges gaps. Moreover, at the point where
    we check for a gap, we don't know if we will attempt a back
    or a front merge. Thus, check for gap to prev in a back merge
    attempt and check for a gap to next in a front merge attempt.
    
    Signed-off-by: Jens Axboe <axboe@fb.com>
    [sagig: Minor rename change]
    Signed-off-by: Sagi Grimberg <sagig@mellanox.com>

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Thread

[PATCH] storvsc: do not assume SG list is continuous when doing bounce buffers (for 4.1 stable only) Long Li <longli@exchange.microsoft.com> - 2017-08-22 07:40 +0200
  Re: [PATCH] storvsc: do not assume SG list is continuous when doing  bounce buffers (for 4.1 stable only) Christoph Hellwig <hch@infradead.org> - 2017-08-22 08:30 +0200
    RE: [PATCH] storvsc: do not assume SG list is continuous when doing  bounce buffers (for 4.1 stable only) Long Li <longli@microsoft.com> - 2017-08-22 21:20 +0200
      Re: [PATCH] storvsc: do not assume SG list is continuous when doing  bounce buffers (for 4.1 stable only) Christoph Hellwig <hch@infradead.org> - 2017-08-23 08:50 +0200
        Re: [PATCH] storvsc: do not assume SG list is continuous when doing  bounce buffers (for 4.1 stable only) Greg KH <gregkh@linuxfoundation.org> - 2017-08-23 15:50 +0200
        Re: [PATCH] storvsc: do not assume SG list is continuous when doing bounce buffers (for 4.1 stable only) "Martin K. Petersen" <martin.petersen@oracle.com> - 2017-08-23 17:30 +0200

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