From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: with ECARTIS (v1.0.0; list xfs); Sun, 21 Sep 2008 21:14:50 -0700 (PDT) Received: from relay.sgi.com (netops-testserver-3.corp.sgi.com [192.26.57.72]) by oss.sgi.com (8.12.11.20060308/8.12.11/SuSE Linux 0.7) with ESMTP id m8M4EhQK010493 for ; Sun, 21 Sep 2008 21:14:44 -0700 Message-ID: <48D71E1E.3010603@sgi.com> Date: Mon, 22 Sep 2008 14:25:02 +1000 From: Lachlan McIlroy Reply-To: lachlan@sgi.com MIME-Version: 1.0 Subject: Re: [PATCH] Remove xfs_iext_irec_compact_full() References: <48D7160B.8020108@sgi.com> <48D71701.6070900@sandeen.net> In-Reply-To: <48D71701.6070900@sandeen.net> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: xfs-bounce@oss.sgi.com Errors-to: xfs-bounce@oss.sgi.com List-Id: xfs To: Eric Sandeen Cc: xfs-dev , xfs-oss Eric Sandeen wrote: > Lachlan McIlroy wrote: >> Yet another bug was found in xfs_iext_irec_compact_full() and while the >> source of the bug was found it wasn't an easy task to track it down because >> the conditions are very difficult to reproduce. Code that is difficult to >> reach is difficult to test and debug. > > It might be nice to give credit to those who helped find it in the commit ;) Not a problem, Eric. And Russell. I don't care who takes the credit - I'm just glad to have this problem fixed. > >> xfs_iext_irec_compact_full() and xfs_iext_irec_compact_pages() are almost >> identical - they both compact indirect extent lists by moving extents from >> subsequent buffers into earlier ones. xfs_iext_irec_compact_pages() only >> moves extents if all of the extents in the next buffer will fit into the >> empty space in the buffer before it. xfs_iext_irec_compact_full() will go >> a step further and move part of the next buffer if all the extents wont fit. >> It will then shift the remaining extents in the next buffer up to the start >> of the buffer. The bug here was that we did not update er_extoff and this >> caused extent list corruption. > > I'd be half-tempted to commit the fix to the code before removing it, > just in case later generations ever resurrect any of this code? *shrug* That did occur to me too. Sounds reasonable. Will do. > > Other than that, I think this looks ok. > > -Eric > >> It does not appear that this extra functionality gains us much. Calling >> xfs_iext_irec_compact_pages() instead will do a good enough job at compacting >> the indirect list and will be quicker too. >> >> For the case in xfs_iext_indirect_to_direct() the total number of extents >> in the indirect list will fit into one buffer so we will never need the >> extra functionality of xfs_iext_irec_compact_full() there. >> >> Also xfs_iext_irec_compact_pages() doesn't need to do a memmove() (the >> buffers will never overlap) so we don't want the performance hit that >> can incur. >> >> --- a/fs/xfs/xfs_inode.c 2008-09-22 13:15:33.000000000 +1000 >> +++ b/fs/xfs/xfs_inode.c 2008-09-22 13:24:24.000000000 +1000 >> @@ -4157,7 +4157,7 @@ xfs_iext_indirect_to_direct( >> ASSERT(nextents <= XFS_LINEAR_EXTS); >> size = nextents * sizeof(xfs_bmbt_rec_t); >> >> - xfs_iext_irec_compact_full(ifp); >> + xfs_iext_irec_compact_pages(ifp); >> ASSERT(ifp->if_real_bytes == XFS_IEXT_BUFSZ); >> >> ep = ifp->if_u1.if_ext_irec->er_extbuf; >> @@ -4488,8 +4488,7 @@ xfs_iext_irec_remove( >> * compaction policy is as follows: >> * >> * Full Compaction: Extents fit into a single page (or inline buffer) >> - * Full Compaction: Extents occupy less than 10% of allocated space >> - * Partial Compaction: Extents occupy > 10% and < 50% of allocated space >> + * Partial Compaction: Extents occupy less than 50% of allocated space >> * No Compaction: Extents occupy at least 50% of allocated space >> */ >> void >> @@ -4510,8 +4509,6 @@ xfs_iext_irec_compact( >> xfs_iext_direct_to_inline(ifp, nextents); >> } else if (nextents <= XFS_LINEAR_EXTS) { >> xfs_iext_indirect_to_direct(ifp); >> - } else if (nextents < (nlists * XFS_LINEAR_EXTS) >> 3) { >> - xfs_iext_irec_compact_full(ifp); >> } else if (nextents < (nlists * XFS_LINEAR_EXTS) >> 1) { >> xfs_iext_irec_compact_pages(ifp); >> } >> @@ -4535,7 +4532,7 @@ xfs_iext_irec_compact_pages( >> erp_next = erp + 1; >> if (erp_next->er_extcount <= >> (XFS_LINEAR_EXTS - erp->er_extcount)) { >> - memmove(&erp->er_extbuf[erp->er_extcount], >> + memcpy(&erp->er_extbuf[erp->er_extcount], >> erp_next->er_extbuf, erp_next->er_extcount * >> sizeof(xfs_bmbt_rec_t)); >> erp->er_extcount += erp_next->er_extcount; >> @@ -4555,91 +4552,6 @@ xfs_iext_irec_compact_pages( >> } >> >> /* >> - * Fully compact the extent records managed by the indirection array. >> - */ >> -void >> -xfs_iext_irec_compact_full( >> - xfs_ifork_t *ifp) /* inode fork pointer */ >> -{ >> - xfs_bmbt_rec_host_t *ep, *ep_next; /* extent record pointers */ >> - xfs_ext_irec_t *erp, *erp_next; /* extent irec pointers */ >> - int erp_idx = 0; /* extent irec index */ >> - int ext_avail; /* empty entries in ex list */ >> - int ext_diff; /* number of exts to add */ >> - int nlists; /* number of irec's (ex lists) */ >> - >> - ASSERT(ifp->if_flags & XFS_IFEXTIREC); >> - >> - nlists = ifp->if_real_bytes / XFS_IEXT_BUFSZ; >> - erp = ifp->if_u1.if_ext_irec; >> - ep = &erp->er_extbuf[erp->er_extcount]; >> - erp_next = erp + 1; >> - ep_next = erp_next->er_extbuf; >> - >> - while (erp_idx < nlists - 1) { >> - /* >> - * Check how many extent records are available in this irec. >> - * If there is none skip the whole exercise. >> - */ >> - ext_avail = XFS_LINEAR_EXTS - erp->er_extcount; >> - if (ext_avail) { >> - >> - /* >> - * Copy over as many as possible extent records into >> - * the previous page. >> - */ >> - ext_diff = MIN(ext_avail, erp_next->er_extcount); >> - memcpy(ep, ep_next, ext_diff * sizeof(xfs_bmbt_rec_t)); >> - erp->er_extcount += ext_diff; >> - erp_next->er_extcount -= ext_diff; >> - >> - /* >> - * If the next irec is empty now we can simply >> - * remove it. >> - */ >> - if (erp_next->er_extcount == 0) { >> - /* >> - * Free page before removing extent record >> - * so er_extoffs don't get modified in >> - * xfs_iext_irec_remove. >> - */ >> - kmem_free(erp_next->er_extbuf); >> - erp_next->er_extbuf = NULL; >> - xfs_iext_irec_remove(ifp, erp_idx + 1); >> - erp = &ifp->if_u1.if_ext_irec[erp_idx]; >> - nlists = ifp->if_real_bytes / XFS_IEXT_BUFSZ; >> - >> - /* >> - * If the next irec is not empty move up the content >> - * that has not been copied to the previous page to >> - * the beggining of this one. >> - */ >> - } else { >> - memmove(erp_next->er_extbuf, &ep_next[ext_diff], >> - erp_next->er_extcount * >> - sizeof(xfs_bmbt_rec_t)); >> - ep_next = erp_next->er_extbuf; >> - memset(&ep_next[erp_next->er_extcount], 0, >> - (XFS_LINEAR_EXTS - >> - erp_next->er_extcount) * >> - sizeof(xfs_bmbt_rec_t)); >> - } >> - } >> - >> - if (erp->er_extcount == XFS_LINEAR_EXTS) { >> - erp_idx++; >> - if (erp_idx < nlists) >> - erp = &ifp->if_u1.if_ext_irec[erp_idx]; >> - else >> - break; >> - } >> - ep = &erp->er_extbuf[erp->er_extcount]; >> - erp_next = erp + 1; >> - ep_next = erp_next->er_extbuf; >> - } >> -} >> - >> -/* >> * This is called to update the er_extoff field in the indirection >> * array when extents have been added or removed from one of the >> * extent lists. erp_idx contains the irec index to begin updating >> >> > >